CN100338478C - Near field electromagnetic positioning system and method - Google Patents

Abstract

A system for measuring distance between a first locus and a second locus includes: (a) at least one beacon device; a respective beacon device of the at least one beacon device being situated at the first locus and transmitting a respective electromagnetic signal; and (b) at least one locator device; a respective locator device of the at least one locator device being situated at the second locus and receiving the respective electromagnetic signal. The respective locator device is situated at a distance from the respective beacon device within near-field range of the respective electromagnetic signal. The respective locator device distinguishes at least two characteristics of the respective electromagnetic signal. The respective locator device employs the at least two characteristics to effect the measuring.

Description

Systems and methods for near-field electromagnetic ranging

technical field

The present invention relates generally to measuring distance or ranging using near-field electromagnetic signal behavior, and more particularly to a system and method for estimating the distance between a transmitter or beacon and a receiver or locator. More particularly, the present invention describes a means for determining the distance to transmit-only beacons without requiring synchronization and without relying on changes in signal amplitude. The present invention can advantageously be used as part of a more general system for determining position (distance and direction) or for tracking (determining position in near real time).

Background technique

related technology

Various techniques are known in the art for determining direction and distance using electromagnetic signals. These techniques are sometimes referred to as wireless direction finding and wireless ranging. Jenkins provides a good summary of the state of the art in wireless orientation. [ Small-Aperture Radio Direction-Finding , by Herndon H. Jenkins; Artech House, Boston; 1991; pp.1-23.]

Arrival time difference and phase difference angle

One technique used for wireless orientation is called time difference of arrival (TDOA). This technique uses a pair of copolar antennas separated by a baseline distance. Incoming signals incident in a direction perpendicular to the baseline are received simultaneously by both antennas. When the direction of incidence is not perpendicular to the baseline, one antenna will receive the signal before the other. The difference in the signal arrival time for each antenna can be related to the angle of incidence. Equivalently, this difference in arrival time can be handled in a similar manner to a difference. Using this technique, the direction of arrival of an incident plane wave can be determined. This TDOA technique can be generalized and applied to networks where the receiving antennas are at known locations. By comparing the arrival times of the signals at each receiving antenna, the direction of the incident plane wave can be determined. In many (but not necessarily all) cases, the incoming plane wave arrives in the direction in which the target transmitter is present. Early examples of such wireless pointing systems include those disclosed by J.S. Stone (U.S. Patent No. 716,134; U.S. Patent No. 716,135; U.S. Patent No. 899,272; U.S. Patent No. 961,265) and Roos (U.S. Patent No. 984,108) . Phase detection for angle of arrival in a manner currently understood in the art is disclosed by Fritz (US Patent No. 2,160,135), by Rung (US Patent No. 2,234,654) and by Budenbom (US Patent No. 2,423,437). 3-D wireless orientation using phase difference is disclosed by Jansky (US Patent No. 2,437,695). Lioio et al. (US Patent No. 5,724,047) disclose a phase and time differential wireless pointing system.

Antenna Pattern Angle of Arrival

Another technique for wireless orientation involves the use of antennas whose response varies as a function of angle. In one implementation, one can use a directional antenna, which has a relatively narrow beamwidth in a particular boresight or direction of maximum signal strength. Change the direction of the antenna until the received signal is maximized so that the axis of the antenna is aligned with the direction of the incoming signal. In an alternative implementation, one could use an antenna that has a null in a particular null direction, or direction of minimum signal strength.

In an earlier invention, Erskine et al. (US Patent No. 1,342,257) disclosed the use of a loop antenna that rotates about an axis lying in the plane of the loop. Robinson (US Patent No. 1,357,210) discloses a similar device which allows finding a minimum or zero when a signal is received. Two loop antennas with orthogonal axes can be electrically combined to create a virtual antenna pointing in the direction of signal maxima (or minima). Bellini (US Patent No. 1,297,313) discloses a capacitive bonding arrangement or goniometer, and Goldschmidt et al. (US Patent No. 1,717,679) discloses a transformer or inductively coupled goniometer. Electrically small loop or electrically small whip (or dipole) antennas can be combined to produce cardiod-type patterns with distinct nulls in particular azimuthal directions. The direction of the antenna can be changed until the received signal is minimized so that the null direction is aligned with the direction of the incoming signal. Examples of this technique are disclosed by Taylor (US Patent No. 1,991,473), Bailey (US Patent No. 1,839,290), and Busignies (US Patent No. 1,741,282). Fischer (US Patent No. 2,539,413) also discloses goniometer techniques combining signals from directional antennas

Amplitude Comparison Angle of Arrival

Another technique for determining the angle of arrival of radio waves is amplitude comparison angle of arrival. Compares the signal amplitudes of two or more antennas to determine the angle of arrival. For example, if the signal amplitude of the first antenna is large and the signal amplitude of the second antenna is small, one can infer that the radio wave arrives from the direction of the maximum value of the pattern of the first antenna and the minimum value of the pattern of the second antenna. If the signals are comparable in magnitude, radio waves may arrive from directions where the pattern of the two antennas has comparable directivity. This is similar to the conventional goniometer angle-of-arrival technique already mentioned. Examples of such techniques include those disclosed by Earp (US Patent No. 2,213,273), Wagstaffe (US Patent No. 2,213,874), Budenbom (US Patent No. 2,234,587), and Clark (US Patent No. 2,524,768).

Doppler angle of arrival

Another technique for wireless orientation utilizes the Doppler-Fizeau effect. If a receiving antenna is rotated at high speed about an axis perpendicular to the direction of an incoming signal, then that incoming signal becomes more frequent as the receiving antenna moves in the direction of the incoming signal, and becomes less frequent as the receiving antenna moves away from the direction of the incoming signal. In practice, it is not feasible to rotate the antenna at high enough angular velocity to easily observe this effect. Instead, many receive antennas can be placed in a circle and scanned and sampled sequentially at high speed to simulate rotation. Such systems are disclosed by Earp (US Patent No. 2,651,774) and Steiner (US Patent No. 3,025,522).

mixed angle of arrival

The existing techniques discussed above for making angle-of-arrival measurements can be advantageously combined. For example, Edwards et al. (US Patent No. 2,419,946) disclose the combination of magnitude and phase comparison in a wireless pointing system. Murphy et al. (US Patent No. 5,541,608) disclose the incorporation of magnitude and phase comparison in a wireless pointing system. Murphy et al. do not use their disclosed mechanism to measure range or distance, and they do not use the near-field behavior of electromagnetic signals as taught by the present invention.

Triangulation

From a network of two or more dispersed locations, various wireless pointing system measurements allow the location of a target transmitter to be determined. One technique by which this task can be accomplished utilizes triangulation. For example, if the direction to a target transmitter has been determined from three known locations, the bearings for the three directions can be plotted on a graph, with the target transmitter positioned at the intersection of the bearings, or at the intersection of the bearings around the defined triangular region. An example of such a system is disclosed by Maloney et al. (US Patent No. 4,728,959).

wireless ranging

Wireless ranging can be done from a collection of orientation measurements, by triangulation. However, a disadvantage of this existing ranging technique is that even obtaining a single range or distance calculation requires measurements from at least two different locations. In order to obtain a reliable distance determination, the positions must be separated by a baseline, which is a significant fraction of the distance to be measured.

radar

There are various other methods by which distance can be measured. One technique is Radio Detection and Ranging (RADAR), as disclosed by Plaistowe (US Patent No. 2,207,267). Radar technology relies on the scattering of signals from targets. Radar works well in detecting aircraft in the open sky or ships on the surface of the ocean, but radar detection becomes increasingly difficult when the target being tracked is in a cluttered environment full of scatterers that are different from the one you wish to track The cross-section of the target is comparable.

Passive tag (passive tag) ranging

Passive cooperative targets, passive transponders or passive tags yield better performance than that achieved with non-cooperative radar targets. In a passive tag ranging system, a transmitter emits a signal that is received by a passive transponder. Passive transponders take the received energy and transmit the signal again. The retransmitted signal is received at the original transmitter and compared with the originally transmitted signal. This comparison may involve phase, time delay, or other comparisons between transmitted and received signals that enable distance measurements. An example of such a system is disclosed by Lichtenberg et al. (US Patent No. 4,757,315). The disadvantage of passive tag ranging is that the effective range tends to be relatively short due to the low power available from the tag for retransmission.

active transponder ranging

Active cooperative targets are generally more effective in ranging operations than passive targets. Active transponders listen for special interrogaroty signals and respond with special reply signals. The reply signal does not have to be the same frequency as the interrogation signal, and the strength of the return signal is not dependent on the strength of the interrogation signal received by the target. This technique may be referred to as active transponder ranging. The time of travel from the interrogating transmitter to the transponder and back to the receiver can be determined from a phase comparison of the originally transmitted signal and the signal received from the remote transponder. In some embodiments, the phase comparison may be performed by modulation applied to the interrogation signal and the response signal. Knowing the wave velocity of the signal, the movement time can be converted to distance. Examples of transponder-type ranging systems include those developed by Green (US Patent No. 1,750,668), Nicolson (US Patent No. 1,945,952), Gunn (US Patent No. 2,134,716), Holmes (US Patent No. 2,198,113), and Strobel (US Patent No. No. 2,248,727) disclosed content. Deloraine et al. (US Patent No. 2,408,048) disclose a system using time modulated pulses in a transponder ranging system. Nosker (US Patent No. 2,470,787) discloses a system for 3-D position measurement using transponder ranging, and Williams (US Patent No. 3,243,812) discloses a particularly simple transponder system involving a transmitting signal and a receiving transponder Period count for phase comparison between signals. The disadvantage of transponder ranging is that it requires the active target to receive the signal, and the transmission of the return signal is generally affected by some properties of the received interrogation signal.

transmit range only

A simpler transmit-only ranging scheme uses transmit-only targets. One way to implement a transmit-only ranging system is to measure the magnitude of the signal received from a transmitter of known transmit power. This amplitude ranging method of wireless ranging is disclosed by Forest (US Patent No. 749,436; US Patent No. 758,517; US Patent No. 1,183,802). In some cases, the magnitude decreases in a predictable manner with distance to the receiver. For example, in free space, the received power varies with the inverse square of the distance. Knowing the transmitted power, received power and the nature of the antenna, one can infer distance using known relationships such as Friis' law.

Friis' law gives the relationship between transmitted power (P _TX ) and received power (P _RX ) in a far-field RF link:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; RX</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; TX</span>}}\frac{{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; TX</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; RX</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ]</span>$

where G _TX is the transmit antenna gain,

G _RX is the receive antenna gain,

λ is the RF wavelength, and

r is the distance between the transmitter and receiver.

在远场下降(roll off)(即，功率随距离增加而减小)。近场链路不遵守这个关系。近场功率以高于平方倒数的幂下降(rolloff)，典型地四次

或更高的倒数。Power as inverse distance squared

Rolls off in the far field (ie, power decreases with distance). Near-field links do not obey this relationship. The near-field power rolls off at a power higher than the inverse square, typically four times

or higher reciprocal.

This near-field behavior has several important consequences. First, the power available in the near-field link is often much higher than would be predicted from the usual far-field Friis' law relationship. This results in a higher signal-to-noise ratio (SNR) and a better performing link. Second, because the near field has such a relatively fast power roll off, the distance tends to be relatively defined and limited. In this way, the near field system is less likely to interfere with another RF system operating outside the operating distance of the near field system.

Inferring distance from received signal power or amplitude is the most problematic. Despite the difficulties, the amplitude ranging system is still used. For example, Moulin (US Patent No. 5,955,982) discloses a method and apparatus for detecting and locating a person buried under an avalanche, where the signal amplitude is used to locate the avalanche victim.

Various other methods exist by which a receiver can obtain range information from only transmitting targets. Ranger (US Patent No. 1,639,667) discloses the idea of synchronizing oscillators at the transmitter and at the remote receiver. The receiver can compare the number of 360° phase shifts or the number of taps per unit of time to infer the change in distance. In a series of inventions, Gage (US Patent No. 1,825,531; US Patent No. 1,939,685; US Patent No. 1,939,686; Patent No. 1,961,757) discloses transmitting a pair of signals at different frequencies with different propagation characteristics and different decay constants. By comparing the amplitude ratios of the received signals, the distance can be inferred. Runge (US Patent No. 2,134,535) discloses looking at the overlap of direct or reflected rays in the received signal to infer the distance to the transmitter. Herson (US Patent No. 2,314,883) discloses estimating the rate of change in amplitude of a received signal in order to infer distance. Hammerquist (US Patent No. 4,788,548) discloses a multi-channel receiver for phase measurements which allows distance measurements to be made. More recently, Sullivan (US Patent No. 5,999,131) discloses a network of receivers that isolates the direct path signal from the transmitter. Relative phase difference measurements between receivers in the network are converted to differential distance estimates for locating transmitters. Sullivan's system has the disadvantage of requiring a common time reference or synchronization between all receivers in the network.

If the transmitter and receiver are synchronized, then precise phase measurements at the receiver can yield range information, up to a 360° phase uncertainty. In other words, a synchronized receiver can determine the transmitter's position relative to the start and end of the wavelength, but cannot determine whether the transmitter's position is within the distance of (for example) the seventh or eighth or some other wavelength . If the absolute (or reference) position of the transmitter is initially determined by other means, the receiver can track changes in the position of the transmitter relative to the established reference. Precise synchronization is essential to obtain meaningful range information in such systems. Only any clock drift between the transmitting target and the receiver results in a range error. In practice, however, precise synchronization is very difficult and often expensive to achieve.

Transmit-only ranging can also be achieved with asynchronous transmit-only targets using a network of synchronized receivers. Relative differences in received phase can be translated into relative differences in position, subject to 360° phase ambiguity.

All of these transmit-only ranging methods rely on the "far-field" assumption: one must assume that the transmit-only target and the receiver location are at least half a wavelength apart. If the transmitting target and receiver are only within half a wavelength or less of each other, near-field ambiguity makes it difficult to determine precise distances.

The simplicity of a transmit-only ranging system is appealing. However, existing transmit-only ranging systems suffer from significant disadvantages. Some transmit-only ranging systems rely on precise synchronization of a network of receivers, which is often complex, difficult and expensive to implement. To calculate range by multiplying time by signal velocity, some transmit-only ranging systems rely on precise time measurements between transmit and receive. Some transmit-only ranging systems rely on equally difficult synchronization of transmitter and receiver. Some transmit-only ranging systems rely on calibrating the transmitter to a known location before an absolute distance can be determined. Some transmit-only ranging systems rely on predictable variations in range and magnitude that are rarely obtained in the real world.

To the best of the inventor's knowledge, prior art electromagnetic tracking and ranging systems rely on the far field: radiated electromagnetic fields received at distances on the order of wavelengths or (usually) farther. Even inventors such as Ranger (US Patent No. 1,639,667), which discloses operation at distances on the order of wavelengths or smaller, implicitly assume far-field signal behavior. No prior art ranging systems known to the inventors utilize near-field signal phenomena in performing ranging or distance measurements. The present invention advantageously utilizes near-field signal phenomena and does not have the dependencies and disadvantages mentioned in prior art ranging systems.

historical environment

Some of the earliest wireless communication systems involved near-field or inductive coupling. One example involves coupled telegraph signals between a moving train and an adjacent telegraph wire. Following the discovery of Herz (implemented by such innovators as Marconi, Lodge, and Tesla), the overwhelming focus of RF development was on long-range, far-field system. By the standards of the time, the frequency was relatively low. The earliest developments were in the low frequency (LF) band (30kHz-300kHz), and soon progressed to the mid-frequency (MF) band (300kHz-3MHz), with some leading-edge work extending into the high frequency (HF) band (3-30MHz). This work is geared towards something that is purely empirical. Engineers focus on the actual technology used to transmit and receive signals. Little has been done to define or understand the fundamental physics that make radio frequency (RF) technology possible. For example, in 1932 the eminent RF expert Frederic Ternan could say: "The understanding of the mechanisms by which energy is radiated from circuits and the derivation of equations expressing this radiation quantitatively includes concepts unfamiliar to the average engineer" [ Radio Engineering , First Edition, by Frederic Emmons Terman ; McGraw Hill, Book Co. Inc., New York; 1932; p. 494.]. At that time the leading edge of RF technology was just beginning to explore the lower end of the very high frequency (VHF) band (30MHz-300MHz). A textbook from that period provides a spectrogram, which ends with "30,000kHz-60,000kHz: experimental and amateur use; >60,000kHz: no use now" [ Radio Physics Course , Second Edition, by Alfred A. Ghirardi; Farrar & Rinehart, Inc., New York; 1942; p. 330.].

Wireless direction and ranging continues to focus on long-range, far-field applications such as wireless navigation and wireless guidance systems for aircraft. The Japanese homing in on the Honolulu wireless base station during their attack on Pearl Harbor [ Joe Carr's Loop Antenna Handbook , First Edition, by Joseph J. Carr; Universal Radio Research, Reynoldsburg, Ohio; 1999; p.85.] . Only in the 1940's, with the development of radar, did the theoretical emphasis in RF technology catch up with the long empirical emphasis. But by then, the RF frontier had rapidly passed VHF and UHF, and moved to microwaves. LF, MF and even HF bands are increasingly becoming backwaters away from the active attention of most RF engineers.

In short, when RF engineers started actively applying basic electromagnetic theory, RF engineers did not actively focus on applying this theory to the problem of wireless ranging at low frequencies, such as those in the LF, MF, and HF bands. In general, the overwhelming emphasis in RF technology is toward far-field systems that operate beyond the wavelength range rather than near-field systems that operate in the wavelength range of approximately

Low frequencies have certain advantages over high frequencies. Low frequencies tend to diffract better around obstacles, so can be used in non-line-of-sight applications, such as on hills or around buildings. Because of the longer wavelengths associated with lower frequencies, multipath interference is far less of a problem than at high frequencies. Further, lower frequencies tend to be more penetrating to foliage and typical building materials such as wood, brick or concrete. Low frequency RF circuits tend to be easier to manufacture and more robust. Components used at low RF frequencies tend to be less expensive and more readily available than those used at high frequencies.

的远场辐射关系预测的。相比之下，近场中的信号水平比远场中减小得更快，强度上作为

的函数减小。结果，相邻的近场系统间的电磁干扰问题较小，使得在比从通常的远场预测所期望的更小的单元大小中，更容易重用相同的频率。简而言之，电磁场在近场和远场中行为不同，并且发明者已经发现某些电磁参数的连续和可预测的变化可以用作穿过近场到远场途中的信号，以确定范围或距离信息。Operation in the near field in the approximate wavelength range also yields certain advantages. Near-field signal levels tend to be much higher than the inverse square of the distance from the usual

The far-field radiation relationship is predicted. In contrast, the signal level in the near field decreases more rapidly than in the far field, with the magnitude as

function decreases. As a result, electromagnetic interference between adjacent near-field systems is less of a problem, making it easier to reuse the same frequencies in smaller cell sizes than would be expected from usual far-field predictions. In short, electromagnetic fields behave differently in the near and far fields, and the inventors have discovered that continuous and predictable changes in certain electromagnetic parameters can be used as signals en route through the near field to the far field to determine range or distance information.

Despite these near-field advantages, as far as the inventors are aware, no prior art describes a system in which near-field signal phenomena and the predictable behavior of those phenomena as they transition from near-field to far-field behavior are exploited in order to obtain range or distance information.

A need exists for an electromagnetic ranging device and method that can operate asynchronously, requiring no transmitter-to-receiver synchronization, or synchronization in a network of receivers.

There is a further need for an electromagnetic ranging device and method that can operate without awkward and lengthy calibration procedures, potentially useful in a wide variety of propagation environments.

There is another need for an electromagnetic ranging device and method that can be used as part of a location or position tracking system.

There is a further need for a system and method for finding the distance to or the location of an electromagnetic signal source whose location is unknown.

There is a further need for a system and method of electromagnetic ranging that operates using relatively low frequencies and exploits the characteristics of the near field.

Contents of the invention

A system for measuring a distance between a first location and a second location includes: (a) at least one beacon device; each of the at least one beacon device is located at a first location and emits a respective electromagnetic signal; and (b) at least one locator device; each locator device of the at least one locator device is located at the second location and receives respective electromagnetic signals. Each locator device is within a near-field distance of each electromagnetic signal from each beacon device. Each locator device distinguishes at least two characteristics of each electromagnetic signal. Each locator device utilizes at least two features to achieve measurements.

A method for measuring a distance between a first location and a second location includes the steps of: (a): transmitting an electromagnetic signal from a first location; (b) receiving an electromagnetic wave at a second location; (c) in no particular order: (1) detect the first feature of the electromagnetic signal; and (2) detect the second feature of the electromagnetic signal; (d) measure the first feature and the second the difference between the features; and (e) using the difference to calculate the distance.

The electromagnetic ranging device of the present invention uses near-field electromagnetic behavior to measure the distance between the transmitting beacon and the receiving locator. The locator includes: (a) a first receiving antenna sensitive to an electric (E) field, (b) a second receiving antenna sensitive to a magnetic (H) field, (c) for receiving the first receiving antenna from the first receiving antenna. signal, (d) means for receiving a second signal from a second receiving antenna, (e) means for determining the difference between the first signal and the second signal, and (f) for using the difference to determine A measure of the distance from the locator to the beacon.

The present invention demonstrates that the phase difference between electric and magnetic fields can be used to determine the distance to a beacon, such as a transmitter or other source of electromagnetic waves or signals. A typical implementation may determine the distance to the beacon to be between about 0.05λ and 0.50λ, where λ is the wavelength of the electromagnetic signal emitted by the beacon. Higher performance implementations of the invention may operate at distances smaller than 0.05λ and greater than 0.50λ.

It is an object of the present invention to provide an electromagnetic distance measuring device and method which can be operated asynchronously without requiring synchronization from the transmitter to the receiver or in a network of receivers.

It is a further object of the present invention to provide an electromagnetic ranging device and method which can be operated without awkward and lengthy calibration procedures, which is useful in a wide variety of propagation environments.

Another object of the present invention is to provide an electromagnetic ranging device and method which can be used as part of a venue or location tracking system.

A further object of the present invention is to provide a system and method for finding the distance to the source of an electromagnetic wave whose location is unknown or its location.

It is another object of the present invention to provide a system and method of electromagnetic ranging that operates using relatively low frequencies and exploits the characteristics of the near field.

Further objects and features of the present invention will become apparent from the following description and claims, in conjunction with the accompanying drawings illustrating preferred embodiments of the invention, in which like reference numerals are used in the various figures similar components.

Description of drawings

Figure 1 is a graphical representation of the electric and magnetic phase relationships as a function of distance for an ideal electrically small toroid in free space.

Figure 2 is a table relating operating distance to frequency for a near-field ranging system.

3 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic quadrature phases.

4 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic fields in phase.

5 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic phases.

Figure 6 is a schematic diagram of details of a preferred embodiment of a system for near-field ranging by comparing electric and magnetic phases.

Figure 7 is a schematic diagram of a system that combines beacon and locator functions in a single unitary device for near-field ranging by comparing electrical and magnetic phases.

8 is a schematic diagram of a representative antenna configuration for a near-field ranging system having a vertically polarized beacon and a vertically polarized omnidirectional locator.

9 is a schematic diagram of a representative antenna configuration for a near-field ranging system having a horizontally polarized beacon and a horizontally polarized omnidirectional locator.

10 is a schematic diagram of a representative antenna configuration for a near-field ranging system having a vertically polarized beacon and a vertically polarized directional locator.

11 is a schematic diagram of a representative antenna configuration for a near-field ranging system having a horizontally polarized beacon and a horizontally polarized directional locator.

12 is a schematic diagram illustrating details of an exemplary receiver in an electromagnetic ranging system.

13 is a schematic diagram illustrating a near-field ranging system configured according to a fixed beacon-mobile locator structure.

14 is a schematic diagram illustrating a near-field ranging system configured according to a fixed/mobile locator-mobile beacon structure.

15 is a schematic diagram illustrating a near-field ranging system configured according to a reciprocal beacon-locator structure.

16 is a schematic diagram illustrating a near-field ranging system configured using a passive tag structure.

17 is a schematic diagram illustrating a near-field ranging system configured using a near-field remote sensing structure.

Figure 18 is a flowchart illustrating the method of the present invention.

Detailed ways

Invention Overview

The present invention will now be described more fully in detail with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. However, the invention should not be considered limited to the embodiments set forth herein, but rather these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

analysis model

The assumed transmit-only target uses a small loop antenna that behaves like a magnetic dipole in the time domain. The magnetic dipole can be thought of as a small current loop of region A, and is a time-dependent current I=I ₀ T(t), where I ₀ is the initial or characteristic current, and T(t) is the time-dependent. Assume that the dipole lies in the xy plane, centered at the origin, with its axis in the z direction. The magnetic moment m of a dipole is: m=A I ₀ T(t), or m=m ₀ T(t). The magnetic field or "H-field" of this small loop is:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\stackrel{<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; r</span>}}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ]</span>$

and the electric field or "E-field" is:

where r is the distance from the origin, c is the speed of light, _ε0 is the permeability of free space, and the derivative with respect to time is represented by a dot. Assuming a sinusoidal excitation T(t) = sin ωt, where ω is the angular frequency: ω = 2πf. So $T=\mathrm{\&omega;}\cos \mathrm{\&omega;t},$ $T=-{\mathrm{\&omega;}}^2\sin \mathrm{\&omega;t}$

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; )</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; r</span>}}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; ]</span>$

as well as:

分量和第一个场的横向分量(

或 )。人们可以比较第一个场的纵向或径向

分量和第二个场的横向分量(

或

)。人们可以比较第一个场的纵向或径向

分量和第一个场的纵向或径向

分量。人们可以比较第一个场的纵向或径向 分量和第二个场的纵向或径向

分量。人们可以比较第一个场的横向分量( 或 )和第一个场的横向分量( 或

)。人们可以比较第一个场的横向分量(

或

)和第二个场的横向分量(

或

)。这些比较可以包括相位的比较、幅度的比较或其它信号性质的比较。There are various methods by which distance information can be obtained from the near field. For example, one can compare the longitudinal or radial

component and the transverse component of the first field (

or ). One can compare the longitudinal or radial of the first field

component and the transverse component of the second field (

or

). One can compare the longitudinal or radial of the first field

longitudinal or radial of the component and the first field

portion. One can compare the longitudinal or radial of the first field component and the longitudinal or radial direction of the second field

portion. One can compare the transverse component of the first field ( or ) and the transverse component of the first field ( or

). One can compare the transverse component of the first field (

or

) and the transverse component of the second field (

or

). These comparisons may include comparisons of phase, magnitude or other signal properties.

The inventors have found that a particularly advantageous and useful comparison is that of the phase of the electrical component of the electromagnetic wave and the phase of the magnetic component of the electromagnetic wave.

For this ideal small loop of free space, the phase of the electric field (E-field) in degrees as a function of distance is:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 180</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;r</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cot</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{\mathrm{<span\; class="notranslate">\; \&omega;r</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; ]</span>$

The lateral H-field phase in degrees as a function of distance is:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 180</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;r</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; cot</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;r</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; ]</span>$

Note that equation [6] in the distance $r=\frac{1}{2\mathrm{\&pi;}}\mathrm{\&lambda;}$ With branch cutting. The phase change is given by:

These relationships assume measurements in the loop plane (θ = 90°). Similar relationships can be obtained for other directions.

Figure 1 is a graphical representation of the phase relationship of the electric and magnetic fields as a function of distance for an ideal electrically small toroid in free space. In FIG. 1 , a graph 100 includes a magnetic or H-Field phase curve 102 , an electrical or E-Field phase curve 104 , and a phase difference or Δφ curve 106 representing the difference between the curves 102 , 104 . Curves 102, 104, 106 are plotted along a first axis 108 representing phase (preferably in degrees) as a function of distance on a second axis 110 at the wavelength of the electromagnetic signal under consideration (preferably in degrees Kilogram-meter-second units, such as meters). As such, the relationship of equations [6]-[8] is illustrated in graphical representation 100 . The H-Field phase curve 102 described by equation [7] starts out 90° out of phase with respect to the E-Field phase curve 104 described by equation [6]. When the distance increases from about 0.05λ to about 0.50λ, the H-Field phase curve 102 starts to decrease and then increases. Similarly, the E-Field phase curve 104 initially increases gradually as the distance increases from approximately 0.05λ to approximately 0.50λ, and increases at an increasing rate as the distance increases. The difference between the E-Field phase curve 104 and the H-Field phase curve 102 is represented by the Δφ curve 106 . The Δφ curve 106 starts at approximately 90° (ie, in quadrature phase) in the near field within a distance of 0.05λ, and reaches 0° (ie, in phase) as the far field approaches for distances beyond 0.50λ. The Δφ curve 106 is mathematically described in equation [8]. Between about 0.05λ and about 0.50λ, the transition of Δφ curve 106 from quadrature phase to in-phase phase is substantially continuous and predictable, and is advantageously used by the present invention. With more precise measurements, this phase shift can be used to benefit within a distance of 0.05λ and beyond 0.50λ.

Equation [8] expresses the phase difference Δφ as a function of distance (r). Equation [8] is a transcendental relation which cannot be reversed to yield an expression for distance as a function of difference. However, there are various mathematical methods that can be used to determine the distance given the phase difference. Equation [8] may be advantageously utilized by other mathematical methods, by way of example and not limitation, such as numerical solving, generation of look-up tables, graphical solving.

In the far field, at distances greater than one wavelength, both the electric and magnetic fields are in phase synchronization. At the limit of the far field, at a fixed rate of 360° per wavelength, the phase of each field changes in step with the other. This is the usual relationship expected by those skilled in the RF art. As a rule, in the prior art, the near-field phase irregularities exploited by the preferred embodiments of the present invention are rarely discussed at all. An exception to this rule is the work of one of the inventors. [ Electromagnetic Energy Around Hertzain Dipoles , by H. Schantz; IEEE Antennas and Propagation Magazine, April 2001; pp.50-62.]

Figure 2 is a table relating distance of operation to frequency for a near-field ranging system. In FIG. 2, a table 200 relates frequencies to selected distances in terms of the wavelength of the signal under consideration. The important feature of the present invention is that the phase difference Δφ between electric and magnetic fields can be used to determine the distance from the locator receiver to the beacon transmitter or other electromagnetic wave sources. This near-field ranging method allows precise determination of the distance to the beacon between approximately 0.05λ and 0.50λ, where λ is the wavelength of the electromagnetic signal emitted by the beacon. Optimal performance is obtained in the range from a distance of about 0.08λ to a distance of about 0.30λ from the beacon. Using more precise measurements, this phase change can be used for distances within 0.05λ and beyond 0.50λ. The corresponding characteristic operating distances as a function of frequency are provided in table 200 of FIG. 2 . Lower frequencies allow operation over longer distances; higher frequencies are better for shorter distances. The specific frequencies listed in table 200 (FIG. 2) are provided for illustration and not for limitation.

Determining the distance from the phase difference Δφ between the electric and magnetic fields may be more complicated than the free-space result indicated by equation [8]. In practice, one may wish to use more sophisticated analytical or computational models (e.g., models including effects propagating on the actual ground rather than in free space), or to use experimental data from the environment in which one wishes to perform ranging operations, to Calibrate the ranging system.

The present invention allows ranging to at least 3000 feet in the 160-190 kHz band, to at least 900 feet in the AM radio broadcast band, and to shorter distances at higher frequencies. A wide variety of other operating distances can be obtained by using other frequencies. Greater distances can be achieved using lower frequencies. Accuracy within inches is achieved even on the longest distances.

In order to provide a simple illustrative example of the invention, that is, for illustration and not for limitation, this description states mobile beacons and stationary locators, but those skilled in the art will readily recognize that beacons may be stationary And the locator is mobile, or both the beacon and the locator are mobile. To avoid wordiness in the following discussion, sometimes only a single locator and a single beacon are discussed. This should not be so construed as to exclude multiple beacons and locators which are used as part of more complex locating, position determining or tracking systems.

Systems for near-field ranging

3 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic quadrature phases. A ranging system 300 is illustrated in FIG. 3 for near-field ranging by comparing the electrical and magnetic phases of quadrature electrical and magnetic signals (90° out of phase) at close range. Beacon 310 includes transmitter 312 and transmit antenna 337 . The beacon 310 emits an electromagnetic wave or signal 315 having a wavelength λ.

Locator 320 receives electromagnetic signal 315 . The locator 320 includes a first electric field antenna 332 for receiving the E-field signal 301 ; and a second magnetic field antenna 331 for receiving the H-field signal 302 . If the distance 304 between the beacon 310 and the locator 320 is, for example, 0.05λ, then the E-field signal 301 and the H-field signal 302 are approximately 90° out of phase at the antennas 331 , 332 . The locator 320 measures this phase difference Δφ and indicates in the distance indicator 306 that the distance is equal to 0.05λ.

4 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic fields in phase. A ranging system 400 is illustrated in FIG. 4 for near-field ranging by comparing the electrical and magnetic phases of electrical and magnetic signals that are in phase (0° phase difference) at long distances. Beacon 410 includes transmitter 412 and transmit antenna 437 . The beacon 410 emits an electromagnetic wave or signal 415 having a wavelength λ.

Locator 420 receives electromagnetic signal 415 . The locator 420 has a first electric field antenna 432 which receives the E-field signal 401 , and a second magnetic field antenna 431 which receives the H-field signal 402 . If the distance 404 between the beacon 410 and the locator 420 is 0.50λ, then the E-field signal 401 and the H-field signal 402 are about 0° out of phase (in phase). The locator 420 measures this phase difference Δφ and indicates in the distance indicator 406 that the distance is equal to 0.50λ.

The locator 320 or 420 can use the free-space relationship between the phase difference Δφ and the distance r described mathematically in Equation [8], can use a more accurate analytical expression considering the influence of soil and ground propagation, can use the propagation environment Theoretical simulations can either use empirical data on phase difference and distance in a particular propagation environment, or use another basis for determining the relationship between phase difference Δφ and distance r.

Basic structure of a system for near-field ranging

5 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic phases. A ranging system 500 for near-field ranging by comparing the electrical and magnetic phases of the electrical and magnetic signals is illustrated in FIG. 5 . Beacon 510 includes transmitter 512 and transmit antenna 536 . Beacons 510 may be mobile or stationary, even unknown or uncooperative sources of electromagnetic radiation in the form of electromagnetic signals. Transmit antenna 536 may be a loopstick antenna or other type of antenna that is substantially immune to changes in the adjacent propagation environment. Transmit antenna 536 may also be a whip antenna as large as permitted by relevant regulations or restrictions imposed by a particular application. The beacon 510 emits an electromagnetic signal 515 .

Locator 520 is located at a distance r from beacon 510 and receives electromagnetic signal 515 . The locator 520 includes: a first antenna 531 , a first receiver 525 , a second antenna 532 , a second receiver 527 , a signal comparator 580 and a distance detector 590 . Signal comparator 580 receives a first representative signal from first receiver 525 and a second representative signal from second receiver 527 . Signal comparator 580 receives the first and second representative signals, and discriminates the difference between the first and second representative signals. The discerned difference may be a difference in phase, a difference in amplitude, or other difference between the first and second representative signals. Signal comparator 580 generates a third signal that is proportional or related to the difference identified by signal comparator 580 . Distance detector 590 receives the third signal from signal comparator 580 and uses the received third signal to determine the distance r between beacon 510 and locator 520 .

或

之间的差别。In a preferred embodiment of the invention, the first antenna 531 is configured to allow the first receiver 525 to generate a first representative signal, which is provided to the signal comparator 580 as a proportional or representative signal to the first component of the electromagnetic signal 515. sex signal. Further in a preferred embodiment of the present invention, the second antenna 532 is configured to allow the second receiver 527 to generate a second representative signal which is provided to the signal comparator 580 as a ratio or signal for it. The first and second components of the electromagnetic signal 515 may differ in polarization or other detectable property. An advantageous distinction in near-field ranging systems is the longitudinal or radial Components and Transverse Components

or

difference between.

In another preferred embodiment of the present invention, the first antenna 531 is an electrical or E-field antenna, which allows the first receiver 525 to generate a first representative signal, which is provided to the signal comparator 580 as an analog to the electromagnetic signal The first component of 515 is proportional or representative of its signal, and the second antenna 532 is a magnetic or H-field antenna which allows the second receiver 527 to generate a second representative signal which is provided to the signal comparator 580 as A signal proportional to or representative of the second component of the electromagnetic signal 515 .

In most preferred embodiments of the present invention, the first antenna 531 is an H-field antenna, the first receiver 525 is an H-field receiver, the second antenna 532 is an E-field antenna, and the second receiver 527 is an E-field antenna. -field receiver, the signal comparator 580 is a phase detector, and the distance detector 590 uses the phase information received from the signal comparator-phase detector 580 to determine the distance r between the beacon 510 and the locator 520 .

Thus, in most preferred embodiments of the invention, first (H-field) antenna 531 responds to the magnetic or H-field component of electromagnetic signal 515 and allows first (H-field) receiver 525 to detect The magnetic or H-field component of 515 is proportional to the first signal. By way of example and not limitation, antennas responsive to the magnetic or H-field component of electromagnetic signals include loop and loop stick antennas. A first (H-field) receiver 525 receives a signal from a first (H-field) antenna 531 and generates a first representative signal proportional to the magnetic or H-field component of the electromagnetic signal 515 . The representative signal may be, for example, an analog signal having a voltage that is directly proportional to the magnitude of the magnetic or H-field component of the electromagnetic signal 515 . Alternatively, the representative signal may be, for example, a digital signal conveying data pertaining to the magnetic or H-field component of the electromagnetic signal 515 . The first (H-field) receiver 525 may include filtering, amplification, analog-to-digital conversion, and adjustment means as commonly understood by practitioners in the RF arts.

A second (E-field) antenna 532 responsive to the electrical or E-field component of the electromagnetic signal 515 allows the second (E-field) receiver 527 to detect a first Two signals. By way of example and not limitation, antennas responsive to the electrical or E-field component of electromagnetic waves include whip, dipole or monopole antennas. A second (E-field) receiver 527 detects the input signal from a second (E-field) antenna 532 and generates a second signal proportional to the electrical or E-field component of the electromagnetic signal 515 . The representative signal may be, for example, an analog signal whose voltage is directly proportional to the magnitude of the electrical or E-field component of the electromagnetic signal 515 . Alternatively, the representative signal may be, for example, a digital signal conveying data pertaining to the electrical or E-field component of the electromagnetic signal 515 . The second (E-field) receiver 527 may include filtering, amplification, analog-to-digital conversion, and adjustments of the kind commonly understood by practitioners in the RF arts.

If the electromagnetic signal 515 is a single frequency sine wave, it is desirable to use very narrow bandwidth filters for the first (H-field) receiver 525 and second (E-field) receiver 527 in order to minimize noise and maximize Optimize the signal-to-noise ratio. However, it is also important for the filters used in the first (H-field) receiver 525 and the second (E-field) receiver 527 to have a constant bandpass group delay such that the first representative signal and The relative phase characteristics of the second representative signal are stable and predictable. The inventors have advantageously used Bessel filters as a starting point for optimization.

The first (H-field) and second (E-field) antennas 532 are preferably oriented to maximize response to the polarization of the electromagnetic signal 515 . In alternative embodiments, the locator 520 may use additional (H-field) antennas, additional (E-field) antennas, additional H-field receivers, and additional E-field receivers in order to detect multiple polarization, or to detect electromagnetic signals from another direction of incidence. Because the electromagnetic signal 515 has near-field characteristics, the polarization may advantageously include longitudinal polarization, which has a component parallel to the direction of propagation of the incident electromagnetic signal.

Signal comparator 580 (preferably implemented in a phase detector) obtains a first representative signal proportional to the magnetic or H-field component of electromagnetic signal 515 and a second representative signal proportional to the electrical or E-field component of electromagnetic signal 515. two representative signals, and the phase difference between the first and second representative signals is determined. Phase detector 580 may be considered (for purposes of illustration and not limitation) as a mixer that receives first and second representative signals and produces proportional quasi-static signal. In an alternative embodiment, phase detector 580 may be implemented with an AND gate that has the first and second representative signals as inputs and whose output is provided to an integrator. The output of the integrator is a quasi-static signal proportional to the quasi-static phase difference between the first representative signal and the second representative signal. The term "quasi-static" in this context means that the change in time is substantially similar to the change in phase, without necessarily having a time or period substantially similar to that of the electromagnetic signal 515 . In other embodiments, phase detector 580 may receive or capture a time domain signal and detect zero crossings or other wave shape characteristics to determine the effective phase difference between the first representative signal and the second representative signal. Suitable phase detectors are readily available - eg, by way of example and not limitation, Analog Devices part no. AD8302. Another embodiment of the phase detector 580 can obtain digital information from the first (H-field) receiver 525 and the second (E-field) receiver 527, and calculate the difference between the first digital information and the second digital information difference.

The distance detector 590 can be implemented in any device capable of converting the measured phase difference to a distance r. In a particularly simple example, distance detector 590 may be an analog voltmeter with a calibrated scale to read distance r as a function of the voltage applied from phase detector 580 . A more complex embodiment of the distance detector 590 may calculate the distance r from the applied voltage received by the phase detector 580, eg preferably using an analog to digital converter and a microprocessor or microprocessor. The distance detector 590 may include a visual, audio or other output to indicate the distance r to the user, or may communicate the measured distance r to the remote end for further analysis as part of an integrated tracking, position determination or positioning system.

The locator 520 may generally be considered to comprise: means for detecting and receiving a first signal; means for detecting and receiving a second signal; means for determining first and second representative and means for determining the distance given the difference between the first and second representative signals.

Beacon 510 may generally be considered to comprise means for emitting an electromagnetic signal. The beacon 510 may be a fixed reference point from which the mobile locator 520 determines the distance or range r. Alternatively, the fixed locator 520 may measure the distance r of the mobile beacon 510 , or the locator 520 may be a mobile unit that measures the distance r of the mobile beacon 510 . Additionally, beacons 510 may be uncooperative transmitters or other sources of electromagnetic signals 515 for which distance r relative to the position of locator 520 is desired to be known.

preferred embodiment

Figure 6 is a schematic diagram of details of a preferred embodiment of a system for near-field ranging by comparing electric and magnetic phases. In FIG. 6 , a ranging system 600 includes a beacon 610 and a locator 620 at a distance r from the beacon 610 . Beacon 610 includes transmitter 612 and transmit antenna 636 , which may be mobile or stationary. Transmitter 612 may include means for altering the nature of transmitted electromagnetic signal 615, including, by way of illustration and not limitation, in response to input or stimulus, such as a control signal received from data bus 695, according to a predetermined pattern, altering the electromagnetic The frequency, phase, polarization or amplitude of the signal 615. In alternative embodiments, transmitter 612 may modulate transmitted electromagnetic signal 615 in order to convey information. Such information may include information identifying the beacon 610 or other information or telemetry of value to the user. For example, binary phase shift keying may be implemented on the transmitted electromagnetic signal 615 without compromising the ranging performance of the present invention. In another embodiment, the transmitter 612 may be turned on or off according to a predetermined pattern in response to a control signal from the data bus 695, or in response to some other input or stimulus. Such inputs or stimuli may include, but are not necessarily limited to, signals from accelerometers, timers, motion detectors, other transducers, or other sensors.

For transmitter 612, it may be beneficial to operate at higher instantaneous power and lower duty cycle in certain applications. For example, transmitter 612 may operate at approximately ten times the allowed average power level, but transmit only 10% of the characteristic period, thus maintaining a substantially similar average transmit power level. Such intermittent operation will enable higher signal-to-noise ratio (SNR) signals. Periodic operation of beacon 610 is also beneficial for operation in the presence of interference. When the beacon 610 is quiet (ie, not transmitting), the locator 620 can characterize a particular source of coherent noise, such as an interfering signal, and can compensate for the presence of this coherent noise once the beacon 610 starts transmitting again.

In applications where security is particularly important, the beacon 610 may use technology to make the electromagnetic signal 615 more difficult to detect by an eavesdropper. These techniques may include frequency modulation methods, periodic operation, varying transmit power to use the minimum power required to make accurate measurements, or other means of providing that signal 615 is not easily detected by an eavesdropper. In smaller cell sizes, transmit power control may be more beneficial to allow frequency reuse.

The first step in determining the distance r between the beacon 610 and the locator 620 is for the beacon 610 to emit an electromagnetic signal 615 . In a preferred embodiment, the electromagnetic signal 615 is vertically polarized, but horizontal or alternate polarizations are also usable. To avoid unnecessary complications, the electromagnetic coupling between beacon 610 and locator 620 is described in terms of electromagnetic waves comprising electromagnetic signal 615 . Because the distance r between the beacon 610 and the locator 620 is generally smaller than the wavelength of the electromagnetic signal 615, the electromagnetic signal 615 is not usually decoupled from the radiated electromagnetic wave of the beacon 610, such as at a distance r much greater than one wavelength of the electromagnetic signal 615. as found in the field. It should be understood that the electromagnetic waves comprising electromagnetic signal 615 are generally reactive or coupled electromagnetic waves, rather than radiating or decoupled electromagnetic waves.

Locator 620 receives electromagnetic signal 615 . In a preferred embodiment, the locator 620 includes a first (H-field) channel 625, a second (H-field) channel 626, a third (E-field) channel 627, a local oscillator 650, a first phase detector 681, a second phase detector 682 and a distance detector 690 (including an analog-to-digital (A/D) converter 691 and a microprocessor 692). An optional data bus 695 may be used to provide a means for exchanging control and data signals between multiple beacons and locators (not shown in detail in Figure 6).

The first (H-field) channel 625 includes a first (H-field) antenna 630, a first (H-field) preselection filter 6400, a first (H-field) mixer 6420, a first (H-field) field) main IF filter 6430, first (H-field) main IF amplifier 6440, first (H-field) sub-IF filter 6450, first (H-field) sub-IF amplifier 6460, and first (H-field) sub-IF amplifier 6460, and first (H-field) sub-IF amplifier 6440 field) Automatic Gain Control 6480. The first (H-field) channel 625 has a first (H-field) antenna port 6270, a first (H-field) adjustment port 6230, a first (H-field) received signal strength indicator (RSSI) port 6220 and The first (H-field) signal output port 6210 .

The second (H-field) channel 626 includes a second (H-field) antenna 631, a second (H-field) preselection filter 6401, a second (H-field) mixer 6421, a second (H-field) field) main IF filter 6431, second (H-field) main IF amplifier 6441, second (H-field) secondary IF filter 6451, second (H-field) secondary IF amplifier 6461, and second (H-field) secondary IF amplifier 6461 and second (H-field) secondary IF amplifier 6441 field) automatic gain control 6481. The second (H-field) channel 626 has a second (H-field) antenna port 6271, a second (H-field) adjustment port 6231, a second (H-field) received signal strength indicator (RSSI) port 6221 and The second (H-field) signal output port 6211 .

The third (E-field) channel 627 includes a third (E-field) antenna 632, a third (E-field) preselection filter 6402, a third (E-field) mixer 6422, a third (E-field) -field) main IF filter 6432, third (E-field) main IF amplifier 6442, third (E-field) sub-IF filter 6452, third (E-field) sub-IF amplifier 6462, and third (E-field) sub-IF amplifier 6462 -field) Automatic Gain Control 6482. The third (E-field) channel 627 has a third (E-field) antenna port 6272, a third (E-field) adjustment port 6232, a third (E-field) received signal strength indicator (RSSI) port 6222 and The third (E-field) signal output port 6212 .

The first (H-field) antenna 630 is responsive to the magnetic or H-field component of the electromagnetic signal 615 and provides a received signal proportional to the magnetic or H-field component of the electromagnetic signal 615 to the first (H-field) preselection filter device 6400.

A first (H-field) preselection filter 6400 passes a first representative signal proportional to the magnetic or H-field component of the electromagnetic signal 615, but rejects signals with unwanted frequencies. The first (H-field) preselection filter 6400 may be, for example, a bandpass filter or a lowpass filter. Typically the first (H-field) pre-selection filter 6400 will pass the frequencies within which the beacon 610 can transmit electromagnetic signals 615 for the application concerned. The choice of frequency band will depend on various factors including, but not necessarily limited to, regulatory constraints, propagation behavior of electromagnetic signal 615, and desired operating distance r.

The first (H-field) mixer 6420 mixes the first representative signal received from the first (H-field) preselection filter 6400 with the local oscillator signal generated by the local oscillator (LO) 650 , to generate the first intermediate frequency (or IF) representative signal. The local oscillator 650 can be a traditional sine wave oscillator, a direct digital synthesizer (Direct Digital Synthesizer, DDS) or other oscillator or waveform template source.

The first main (H-field) IF filter 6430 accepts only the desired first IF representative signal and rejects other unwanted signals. A crystal filter can advantageously be used as the first main (H-field) IF filter 6430 . Such crystal filters are characterized by an extremely narrow passband and more preferably have a constant group delay within the passband. The narrow passband acts to allow the desired first IF representative signal to pass to the first main (H-field) IF amplifier 6440 while rejecting adjacent unwanted signals. The first main (H-field) IF amplifier 6440 amplifies the amplitude of the first IF representative signal and communicates the amplified first IF representative signal to the first (H-field) IF filter 6450 . First time (H-field) IF filter 6450 accepts only wanted first IF representative signals and rejects other unwanted signals. A crystal filter can advantageously be used as the first (H-field) IF filter 6450 . Such crystal filters are characterized by an extremely narrow passband and more preferably have a constant group delay within the passband. The narrow passband acts to allow the desired first IF representative signal to pass to the first (H-field) IF amplifier 6460, while rejecting adjacent unwanted signals. The first time (H-field) IF amplifier 6460 increases the amplitude of the first IF representative signal and communicates the first IF representative signal to the signal output port 6210 and to the first automatic gain control (AGC) 6480 .

The first automatic gain control 6480 adjusts the gain of the first main (H-field) IF amplifier 6440 and the first first (H-field) IF amplifier 6460 to maintain the desired level of the first IF representative signal. By dividing the desired overall gain between the first main (H-field) IF amplifier 6440 and the first (H-field) IF amplifier 6460, it is possible to achieve higher stability and reliability than in a single amplification stage alone. maintain high overall gain and large dynamic range. Similarly, by splitting the desired filtering between the first main (H-field) IF filter 6430 and the first (H-field) IF filter 6450, higher Stability and reliability enable a narrower passband. The first automatic gain control 6480 more preferably includes a received signal strength indicator (RSSI), and communicates the RSSI level to the RSSI output 6220 .

The second (H-field) antenna 631 is responsive to the magnetic or H-field component of the electromagnetic signal 615 and provides a received signal proportional to the magnetic or H-field component of the electromagnetic signal 615 to the second (H-field) preselection filter device 6401.

A second (H-field) preselection filter 6401 passes a first representative signal proportional to the magnetic or H-field component of the electromagnetic signal 615, but rejects signals with unwanted frequencies. The second (H-field) pre-selection filter 6401 may be, for example, a band-pass filter or a low-pass filter. Typically the second (H-field) pre-selection filter 6401 will pass the frequencies within which the beacon 610 can transmit electromagnetic signals 615 for the application concerned. The choice of frequency band will depend on various factors including, but not necessarily limited to, regulatory constraints, propagation behavior of electromagnetic signal 615, and desired operating distance r.

The second (H-field) mixer 6421 mixes the first representative signal received from the second (H-field) pre-selection filter 6401 with the local oscillator signal generated by the local oscillator (LO) 650 , to generate a second intermediate frequency (or IF) representative signal. Local oscillator 650 may be a conventional sine wave oscillator, direct digital synthesizer (DDS), or other oscillator or waveform template source.

The second main (H-field) IF filter 6431 accepts only the desired second IF representative signal and rejects other unwanted signals. A crystal filter can advantageously be used as the second main (H-field) IF filter 6431 . Such crystal filters are characterized by an extremely narrow passband and more preferably have a constant group delay within the passband. The narrow passband acts to allow the desired second IF representative signal to pass to the second main (H-field) IF amplifier 6441 while rejecting adjacent unwanted signals. The second primary (H-field) IF amplifier 6441 amplifies the amplitude of the second IF representative signal and delivers the amplified second IF representative signal to the second secondary (H-field) IF filter 6451 . Second order (H-field) IF filter 6451 accepts only desired second IF representative signals and rejects other unwanted signals. A crystal filter can advantageously be used as the second order (H-field) IF filter 6451 . Such crystal filters are characterized by an extremely narrow passband and more preferably have a constant group delay within the passband. The narrow passband acts to allow the desired second IF representative signal to pass to the second (H-field) IF amplifier 6461 while rejecting adjacent unwanted signals. The second sub (H-field) IF amplifier 6461 increases the amplitude of the second IF representative signal and communicates the second IF representative signal to the signal output port 6211 and to the second automatic gain control (AGC) 6481 .

The second automatic gain control 6481 adjusts the gain of the second primary (H-field) IF amplifier 6441 and the second secondary (H-field) IF amplifier 6461 to maintain the desired level of the second IF representative signal. By dividing the desired overall gain between the second main (H-field) IF amplifier 6441 and the second (H-field) IF amplifier 6461, it is possible to achieve higher stability and reliability than in a single amplification stage alone. maintain high overall gain and large dynamic range. Similarly, by splitting the desired filtering between the second primary (H-field) IF filter 6431 and the second secondary (H-field) IF filter 6451, higher Stability and reliability for narrower passbands. The second automatic gain control 6481 more preferably includes a Received Signal Strength Indicator (RSSI), and communicates the RSSI level to the RSSI output 6221 .

The third (E-field) antenna 632 responds to the electrical or E-field component of the electromagnetic signal 615 and provides a received signal proportional to the electrical or E-field component of the electromagnetic signal 615 to the third (E-field) preselection filter device 6402.

A third (E-field) preselection filter 6402 passes a third representative signal proportional to the electrical or E-field component of the electromagnetic signal 615, but rejects signals with unwanted frequencies. The third (E-field) preselection filter 6402 may be, for example, a bandpass filter or a lowpass filter. Typically the third (E-field) pre-selection filter 6402 will pass the frequencies within which the beacon 610 can transmit electromagnetic signals 615 for the application concerned. The choice of frequency band will depend on various factors including, but not necessarily limited to, regulatory constraints, propagation behavior of electromagnetic signal 615, and desired operating distance r.

The third (E-field) mixer 6422 mixes the third representative signal received from the third (E-field) pre-selection filter 6402 with the local oscillator signal generated by the local oscillator 650 (LO) , to generate a third intermediate frequency (or IF) representative signal. Local oscillator 650 may be a conventional sine wave oscillator, direct digital synthesizer (DDS), or other oscillator or waveform template source.

The third main (E-field) IF filter 6432 accepts only the desired third IF representative signal and rejects other unwanted signals. A crystal filter can advantageously be used as the third main (E-field) IF filter 6432 . Such crystal filters are characterized by an extremely narrow passband and more preferably have a constant group delay within the passband. The narrow passband acts to allow the desired third IF representative signal to pass to the third main (E-field) IF amplifier 6442 while rejecting adjacent unwanted signals. A third primary (E-field) IF amplifier 6442 amplifies the magnitude of the third IF representative signal and communicates the amplified third IF representative signal to a third secondary (E-field) IF filter 6452 . Tertiary (E-field) IF filter 6452 accepts only the desired third IF representative signal and rejects other unwanted signals. A crystal filter can advantageously be used as the third order (E-field) IF filter 6452 . Such crystal filters are characterized by an extremely narrow passband and more preferably have a constant group delay within the passband. The narrow passband acts to allow the desired tertiary IF representative signal to pass to the tertiary (E-field) IF amplifier 6462 while rejecting adjacent unwanted signals. The third (E-field) IF amplifier 6462 increases the amplitude of the third IF representative signal and communicates the third IF representative signal to the signal output port 6212 and to the third automatic gain control (AGC) 6482 .

The third automatic gain control 6482 adjusts the gain of the second main (E-field) IF amplifier 6442 and the third (E-field) IF amplifier 6462 to maintain the desired third IF representative signal level. By dividing the desired overall gain between the third main (E-field) IF amplifier 6442 and the third (E-field) IF amplifier 6462, it is possible to achieve higher stability and reliability than in a single amplification stage alone. maintain high overall gain and large dynamic range. Similarly, by splitting the desired filtering between the third primary (E-field) IF filter 6432 and the third (E-field) IF filter 6452, higher Stability and reliability for narrower passbands. The third automatic gain control 6482 preferably includes a received signal strength indicator (RSSI), and communicates the RSSI level to the RSSI output 6222 .

The local oscillator 650 may also be advantageously used as a tuner to select among the plurality of electromagnetic signals 615 transmitted by the plurality of beacons 610 . A particular beacon 610 that emits a particular electromagnetic signal 615 can be distinguished from other beacons 610 that emit other electromagnetic signals 615 at slightly different frequencies. In this way, a single locator 620 can track many different beacons 610 . Various other methods for tracking multiple beacons 610 are possible including, for example, time division multiple access. If the beacon 610 modulates the transmitted electromagnetic signal 615 with identification information, one can distinguish between multiple beacons 610 operating on the same frequency. Similarly, many different locators 620 can measure the distance r to the common beacon 610 .

While synchronization between beacons 610 and locators 620 is not required, a common local oscillator 650 functions to maintain synchronization among multiple channels 625 , 626 , 627 within a single locator 620 . Synchronization among the multiple channels 625,626,627 within the locator 620 is advantageous to enable accurate phase comparisons between the signals received by the multiple channels 625,626,627.

In other embodiments, local oscillator 650 may tune first channel 625, second channel 626, or third channel 627 (or various combinations of channels 625, 626, 627) to sweep various frequencies of interest. Microprocessor 692 can monitor and compile data from RSSI ports 6220, 6221, 6222 (or various combinations of RSSI ports 6220, 6221, 6222) to characterize the noise and interference environment. Microprocessor 692 may communicate appropriate control signals to plurality of beacons 610 via data bus 695 to select the optimum operating frequency and mode given the characteristic noise and interference environment. Similarly, in a dense signal environment where there are many beacons 610 operating simultaneously, the microprocessor 692 can monitor the signal and communicate appropriate control signals to the multiple beacons 610 via the data bus 695 for the convenience of multiple beacons 610 Coexistence within or between multiple beacons 610 allocates optimal operating frequencies and modes. In addition, the microprocessor 692 can monitor the distance r, and communicate appropriate control signals to each beacon 610 through the data bus 695, so as to assign the optimal operating frequency and mode suitable for each beacon 610 to each beacon 610, so that each beacon The marker 610 is adapted to work at a detected distance r.

In other embodiments, channels other than channels 625, 626, 627 may be used such that locator 620 may simultaneously track multiple beacons 610 generating electromagnetic signals 615 at different frequencies. Furthermore, additional channels can be advantageously utilized to detect and characterize noise and interference environments. In other embodiments, additional channels associated with alternate polarizations may enable ranging system 600 to make measurements without compromising the relative orientation of beacon 610 with respect to locator 620 .

In the ranging system 600 (FIG. 6), the first phase detector 681 receives the first IF representative signal from the first signal output port 6210, and receives the third IF representative signal from the third signal output port 6212, And a phase difference between the first and third IF representative signals is determined. The second phase detector 682 receives the second IF representative signal from the second signal output port 6211, and receives the third IF representative signal from the third signal output port 6212, and determines the second and third IF representative signals difference between. In a preferred embodiment, the locator 620 has two H-field channels (a first (H-field) channel 625 and a second (H-field) channel 626 ) and a third (E-field) channel 627 . In a preferred embodiment using vertically polarized electromagnetic signals 615, the third electrical antenna 632 is a vertical whip antenna having an omnidirectional pattern in a first plane perpendicular to the axis of the whip. In a preferred embodiment, the magnetic antennas 630, 631 are loop antennas having an omnidirectional pattern in a second plane substantially perpendicular to the first plane (associated with the whip antenna of the third electric antenna 632). To obtain sensitivity to the magnetic component of the electromagnetic signal 615 incident in any direction, it is advantageous to have two magnetic antennas 630, 631. If there is only one magnetic antenna 630 or 631 , the locator 620 tends to be insensitive to a beacon 610 located in the null direction of the single magnetic antenna 630 or 631 . By having two magnetic antennas 630, 631, the locator 620 can determine the distance r to the beacon 610 in any direction. An additional advantage of having two magnetic antennas 630, 631 is that, in addition to distance information, the locator 620 can obtain angle of arrival information using existing techniques.

For optimum performance of the phase detectors 681, 682, it is advantageous that the amplitudes of the first, second and third IF representative signals remain within desired amplitude limits. Automatic gain controls 6480, 6481, 6482 function to maintain the desired amplitude limit for the first, second and third IF representative signals. The phase detectors 681, 682 can utilize logarithmic amplifiers to maintain a constant signal level as used in Analog Devices part no. AD8302 (Phase Detector IC). Alternatively, channels 625, 626, 627 may include limiters (not shown in Figure 6) to limit the output signal level.

The distance detector 690 converts the measured phase difference received from the phase detectors 681, 682 into a distance r. In a preferred embodiment, the distance detector 690 includes an analog-to-digital converter 691 and a microprocessor (or microcontroller) 692 that cooperate to calculate the distance from signals received from one or both of the phase detectors 681, 682. r. In a preferred embodiment, distance detector 690 also monitors RSSI levels from RSSI ports 6220, 6221, 6222, so that distance detector 690 can select either (or both) of phase detectors 681, 682 when determining distance r use. Distance detector 690 may also compare RSSI levels from RSSI ports 6220 , 6221 , 6222 to determine the angle of arrival of electromagnetic signal 615 . Generally, if the beacon 610 is located in the pattern of the first magnetic field antenna 630, then the first phase detector 681 is preferred; and if the beacon 610 is located in the pattern of the second magnetic field antenna 631, the first phase detector is preferred. 682. Ideally, the distance detector 690 will selectively utilize the signals received from the phase detectors 681, 682 to optimize the distance measurement. Such optimization may also include, for example, a locator 620 that combines signals received from the magnetic field antennas 630, 631 to generate antenna patterns that nullify interfering signals or maximize desired signals. The RSSI levels from the RSSI ports 6220, 6221, 6222 may also be used by the distance detector 690 to supplement or complement the information from the phase detectors 681, 682 when determining the distance r.

The distance detector 690 may include a form of video, audio or other output to indicate the distance r to the user, or may communicate the measured distance to the remote end for further analysis as part of an integrated positioning, tracking or location system. The distance detector 690 may also include means for controlling the local oscillator 650, including (but not necessarily limited to) setting the frequency of the local oscillator signal.

Data bus 695 is optional and, when used, allows data and control signals to be communicated between beacon 610 and locator 620 . Data bus 695 may include a wireless network (eg, an 802.11b network), a hard-wired network (eg, an Ethernet connection or a serial cable), or may utilize modulation of electromagnetic signal 615 emitted by beacon 610 . Multiple locators 620 and beacons 610 may share a common data bus 695 . Such multiple locators 620 and beacons 610 may work in conjunction to create an integrated tracking, position determination or positioning system. Using the wireless data bus 695, the beacon 610 is no longer strictly a transmitting-only device. Because only the transmitted electromagnetic signal 515 is necessary for the electromagnetic ranging system, the precise timing of the wireless data link required by conventional transponder ranging systems can be eliminated. Timing information can be communicated over a wireless data link.

It can be considered that the locator 620 comprises: means for detecting or receiving a first (H-field) signal; means for detecting or receiving a second (H-field) signal; means for detecting or receiving a third (E -field) signal; means for determining a first phase difference between the first and third signals; means for determining a second phase difference between the second and third signals; and means for giving the first Determine the distance r when differing from the second phase. The locator 620 may also advantageously include means for adjusting the locator 620 so that distance data for any one of the plurality of beacons 610, each generating an electromagnetic signal at a different frequency, may be obtained.

Still further advantages may arise by adding to the locator 620 means for communicating data between the plurality of locators 620 and the plurality of beacons. Such means (eg, data bus or wireless link 695) may advantageously be used in an integrated tracking, positioning or positioning system.

It should be kept in mind that the functions and elements of positioner 620 need not be implemented in a single unit. For example, it may be advantageous to place the first (H-field) antenna 630, the second (H-field) antenna 631 and the third (E-field) antenna 632 at respective locations away from other elements and functional blocks of the locator 620 superior. If remoteness is desired for safety reasons, economical reasons, operational reasons, ease of use or any other reason, the antenna can be connected eg by an RF cable. Similarly, locator 620 may enable signal detection and reception at one location and phase detection at another location. The locator 620 can also perform phase detection at one location and transmit data to the remote distance detector 690 for distance r determination.

combined beacon-locator

Figure 7 is a schematic diagram of a system for near-field ranging by comparing electric and magnetic phases while combining beacon and locator functions in a single single device. In FIG. 7, a combined beacon-locator device 700 is configured to work as a beacon whose distance r to a remote locator (such as a remote beacon-locator device 710 working as a locator) can be determined by the remote locator Measurement. Alternatively, the beacon-locator device 700 may operate as a locator that measures the distance to another beacon (eg, a remote beacon-locator device 710 operating as a beacon).

The beacon-locator device 700 includes: a first magnetic (H-field) antenna 730 , a second (E-field) antenna 732 , a transmit-receive switch 728 , a transmitter 712 and a locator receiver 720 . The locator receiver 720 includes: a first (H-field) receiver 722 , a second (E-field) receiver 742 , a phase detector 781 and a distance detector 790 . An optional data bus 795 allows communication between or among multiple beacon-locators, beacons, locators or other devices.

Combined beacon-locator in locator mode

Remote beacon-locator device 710 (operating in beacon mode) emits an electromagnetic signal 715 which is received by beacon-locator system 700 operating in locator mode. The first (H-field) antenna 730 is sensitive to the magnetic component of the incident electromagnetic signal 715 and conveys a representative magnetic signal proportional to the magnetic component of the electromagnetic signal 715 to the antenna of the first (H-field) receiver 722 port 7270.

A first (H-field) receiver 722 receives a representative magnetic signal at a first antenna port 7270 and a local oscillator signal from a local oscillator 750 at a local oscillator (LO) port 7230 . A first (H-field) receiver 722 provides at a first output port 7210 a first receive intermediate frequency ( IF) representative signal, and RSSI signal is provided at RSSI port 7220.

Because the beacon-locator device 700 is operating in locator mode, the transmit-receive switch 728 is configured to connect the second (E-field) antenna 732 to the second (E-field) receiver 742 . In alternative embodiments, transmit-receive switch 728 may be a circulator or other device that allows a beacon-locator, such as beacon-locator device 700, to operate as both a beacon and a locator. The second (E-field) antenna 732 is sensitive to the electrical component of the incident electromagnetic signal 715 and conveys a representative electrical signal proportional to the electrical component of the electromagnetic signal 715 to the antenna of the second (E-field) receiver 742 port 7271.

The second (E-field) receiver 742 receives the representative electrical signal at the second antenna port 7271 and the local oscillator signal from the local oscillator (LO) 750 at the local oscillator port 7231 . A second (E-field) receiver 742 provides at a second output port 7211 a second receive intermediate frequency ( IF) representative signal, and provide RSSI signal at RSSI port 7221.

Phase detector 781 receives a first representative signal from output port 7210 and receives a second representative signal from output port 7211 . Phase detector 781 generates a phase difference output signal proportional to the phase difference between the first and second representative signals, and communicates the phase difference output signal to distance detector 790 .

The distance detector 790 includes an analog-to-digital converter 791 and a microprocessor 792 . Distance detector 790 receives RSSI signals from RSSI ports 7220 , 7221 , and phase difference output signal from phase detector 781 . The analog-to-digital converter 791 converts these signals into digital signals and communicates them to the microprocessor 792 . The microprocessor 792 calculates the distance r from the digital signal input received from the analog-to-digital converter 791 . Methods by which the distance r can be determined by its microprocessor 792 are, for example: 1) the free space theory provided in equation [8], 2) more accurate analytical or numerical models including other effects of the ground and propagation environment, and 3) ) based on empirically measured models. The distance r can be calculated from the phase input only or using a more complex model including input from the RSSI ports 7220,7221.

The microprocessor 792 can adjust the frequency of the local oscillator 750 to tune the first (H-field) receiver 722 and the second (E-field) receiver 742 . This enables the beacon-locator device 700 to measure the distance r of various other beacons 710 or beacon-locators 700 operating at different frequencies. Microprocessor 792 also enables beacon-locator device 700 to use a frequency hopping system or power control scheme for additional safety and robustness.

Microprocessor 792 may have user interface means, such as an audio or visual display, to provide distance measurements to the user. Additionally, the microprocessor 792 may communicate distance or other information to another location via the optional data bus 795 as part of an integrated system relying on tracking and positioning inputs, or for other purposes.

The exemplary beacon-locator device 700 has two channels: a first (H-field) receiver 722 and a second (E-field) receiver 742 . If better performance is desired, additional channels may be preferred at the expense of additional complexity and cost. Such additional channels may be used to detect E-field and H-field components in alternating polarizations, including but not limited to polarization components along the direction of the incident electromagnetic signal 715 . In this way, the beacon-locator device 700 may be less dependent on the particular direction of the incident electromagnetic signal 715 and thus provide more robust performance. The same benefit arises for a locator that is not combined with a beacon to form a beacon-locator.

Combined beacon-locator in beacon mode

When the beacon-locator device 700 is operating in the beacon mode, the microprocessor 792 activates the transmit-receive switch 728 to connect the transmitter 712 to the antenna 732 . Microprocessor 792 also sets the appropriate frequency for transmitter 712 . Exemplary beacon-locator device 700 uses electrical antenna 732 as a beacon transmitting antenna. The magnetic antenna 730 is ready to be used. The selection of an antenna to be used for transmit operation in beacon mode depends on several factors including, for example, pattern, performance in the vicinity of other objects, polarization, matching, and propagation environment.

The remote beacon-locator device 710 includes an electrical antenna 735 and a magnetic antenna 733 . Transmitter 712 sends RF signals to transmit antenna 732 . Transmit antenna 732 radiates an electromagnetic signal 716 which is received by electrical antenna 735 and by magnetic antenna 733 when remote beacon-locator device 710 is operating in locator mode. The remote beacon-locator device 710 receives the H-field signal from the magnetic antenna 733 and the E-field signal from the electric antenna 735, thus allowing the remote beacon-locator device 710 to determine to the beacon-locator device 700 The distance r.

Optional data bus 795 allows beacon-locator device 700 to interact and cooperate with remote beacon-locator device 710 . For example, beacon-locator device 700 may trigger remote beacon-locator device 710 to cause remote beacon-locator device 710 to transmit and allow beacon-locator device 700 to determine to remote beacon-locator device 710 The distance r. Suitable triggers may include, for example, data regarding communication frequencies, frequency hopping patterns, power control feedback, or other characteristics of the transmit signal to be radiated from the remote beacon-locator device 710 . Triggers may also include identification or authentication information.

Transmitter 712 may be controlled by microprocessor 792 to modulate electromagnetic signal 716 with information. A variety of modulation techniques are possible. Binary Phase Shift Keying (BPSK) is a preferred modulation choice. BPSK is advantageous because of its simplicity. Furthermore, because the present invention relies on the relative difference between the electric and magnetic phases, common mode phase shifts (as occurs with BPSK and similar modulations) do not affect the present invention's ability to measure distance r. Such information may include identification or authentication information, or other information, or telemetry values to the user.

antenna configuration

8-11 show various antenna configurations for ranging systems 800 , 900 , 1000 , 1100 . 8 is a schematic diagram of a representative antenna configuration for a near-field ranging system having a vertically polarized beacon and a vertically polarized omnidirectional locator. In FIG. 8 , a ranging system 800 includes a vertically polarized beacon 810 and a locator 820 . Vertically polarized antenna 836 associated with vertically polarized beacon 810 is typically a vertically oriented whip or dipole antenna, but may be a loop or ring stick antenna, oriented to radiate vertically polarized electromagnetic radiation in a desired direction. Signal 815. In many applications, the omnidirectional coverage of a single vertically oriented whip antenna is superior to the more directional pattern of a conventional vertically polarized loop antenna. The locator 820 includes an electric antenna 832 , a first magnetic antenna 831 , and a second magnetic antenna 833 directed perpendicular to the first magnetic antenna 831 . Electrical antenna 832 is typically a vertically oriented whip or dipole antenna. The first magnetic antenna 831 and the second magnetic antenna 833 are typically loop or loop stick antennas directed in response to the vertically polarized electromagnetic signal 815 . The locator 820 may select the first magnetic antenna 831 or the second magnetic antenna 833 to optimize the received (H-field) signal. The locator 820 may also use both the signal from the first magnetic antenna 831 and the signal from the second magnetic antenna 833 .

9 is a schematic diagram of a representative antenna configuration for a near-field ranging system with a horizontally polarized beacon and a horizontally polarized omnidirectional locator. In FIG. 9 , a ranging system 900 includes a horizontally polarized beacon 910 and a locator 920 . The horizontally polarized antenna 937 associated with the horizontally polarized beacon 910, typically a vertically oriented ring stick or loop directional antenna directed in the horizontal plane, but may be a whip or dipole antenna, is oriented to point in the desired direction A horizontally polarized electromagnetic signal 915 is radiated. In many applications, the omnidirectional coverage of a single loop or loop stick antenna is superior to the more directional pattern of a conventional horizontally polarized whip or dipole antenna. The locator 920 includes a magnetic antenna 931 , a first electrical antenna 932 and a second electrical antenna 934 . The magnetic antenna 931 is typically a ring-rod or loop-oriented antenna oriented vertically in the horizontal plane. The first electrical antenna 932 and the second electrical antenna 934 are typically dipole or whip antennas directed in response to the horizontally polarized electromagnetic signal 915 . The locator 920 may select either the first electrical antenna 932 or the second electrical antenna 934 to optimize the received (E-field) signal. The locator 920 may also use signals from both the first electrical antenna 932 and the second electrical antenna 934 .

10 is a schematic diagram of a representative antenna configuration for a near-field ranging system with vertically polarized beacons and vertically polarized directional locators. In FIG. 10 , a ranging system 1000 includes a vertically polarized beacon 1010 and a locator 1020 . The vertically polarized antenna 1036 associated with the vertically polarized beacon 1010 is typically a vertically oriented whip or dipole antenna directed in a vertical plane, but may be a loop or ring stick antenna directed to point in a desired direction A vertically polarized electromagnetic signal 1015 is radiated. In many applications, the omnidirectional coverage of a single vertically oriented whip antenna is superior to the more directional pattern of a conventional vertically polarized loop antenna. The locator 1020 includes an electrical antenna 1032 and a magnetic antenna 1031 . Electrical antenna 1032 is typically a vertically oriented whip or dipole antenna. Magnetic antenna 1031 is typically a loop or ring rod antenna directed in response to vertically polarized electromagnetic signal 1015 . Locator 1020 typically must be steered to optimize the signal from magnetic antenna 1031 . Additionally, the direction of arrival of the electromagnetic signal 1015 can be determined by directing the null direction of the magnetic antenna 1031 toward the direction of arrival of the electromagnetic signal 1015 and observing the drop in RSSI level. If the responses of the electric antenna 1032 and the magnetic antenna 1031 are summed, the magnitude of the electromagnetic signal 1015 can be determined by orienting the zero direction of the effective summed pattern towards the direction of arrival of the electromagnetic signal 1015 and observing the drop in magnitude of the summed response. Arrival directions.

11 is a schematic diagram of a representative antenna configuration for a near-field ranging system with a horizontally polarized beacon and a horizontally polarized directional locator. The ranging system 1100 in FIG. 11 includes a horizontally polarized beacon 1110 and a locator 1120 . The horizontally polarized antenna 1137 associated with the horizontally polarized beacon 1110 is typically a vertically oriented loop stick or loop antenna oriented in the horizontal plane, but may be a whip or dipole antenna, oriented to The direction radiates a horizontally polarized electromagnetic signal 1115. In many applications, the omnidirectional coverage of a single loop or loop stick antenna is superior to the more selective pattern of a conventional horizontally polarized whip or dipole antenna. Locator 1120 includes electrical antenna 1132 and magnetic antenna 1131 . The electrical antenna 1132 is typically a horizontally oriented whip or dipole antenna. Magnetic antenna 1131 is typically a loop or ring rod antenna directed in response to horizontally polarized electromagnetic signal 1115 . The locator 1120 typically must be steered to optimize the signal from the electrical antenna 1132 . Additionally, the direction of arrival of the electromagnetic signal 1115 can be determined by directing the null direction of the electrical antenna 1132 toward the direction of arrival of the electromagnetic signal 1115 and observing the associated drop in RSSI level. If the responses of the magnetic antenna 1131 and the electric antenna 1132 are summed, by orienting the zero direction of the effective summed pattern towards the direction of arrival of the electromagnetic signal 1115 and observing the drop in magnitude of the associated summed response, the electromagnetic The direction of arrival of signal 1115.

The choice of polarization may be influenced by the details of a particular propagation environment, by the presence of potentially interfering signals of a particular polarization, or by the requirements of a particular application. Vertical polarization is generally preferred for propagation in environments where undesired coupling tends to be horizontal, such as near the ground. Horizontal polarization is generally preferred for propagation in environments where undesired coupling tends to be vertical, such as through vertically oriented sections of steel. Circular polarization is generally preferred for systems where directional independence is important. Some such coupling is actually desirable if this coupling tends to direct electromagnetic waves in the desired direction.

Important antenna parameters for designing a ranging system according to the present invention include: antenna pattern, matching, form factor, performance and cost. Another important parameter is the capture of the incident electromagnetic signal and the discrimination between the electrical and magnetic components of the incident electromagnetic signal. Various suitable antenna options are known to those skilled in the RF arts.

Exemplary Receiver

The inventors have implemented a ranging system as taught by the present invention. This system operates at 10.7 MHz and has ranging accuracy to within inches from about 5 feet to about 35 feet. Since the wavelength (λ) is 92 feet at 10.7MHz, this corresponds to 0.054λ to 0.38λ. Much longer distances are possible by utilizing much lower frequencies according to the teachings of the present invention.

12 is a schematic diagram illustrating details of an exemplary receiver in an electromagnetic ranging system. In FIG. 12 , a ranging system 1200 includes a beacon 1210 and a locator 1220 . Beacons 1210 emit electromagnetic signals 1215 that are received by locators 1220 . Locator 1220 includes an electrical antenna 1232 that is sensitive to the electrical component of electromagnetic signal 1215 . Electrical antenna 1232 detects a first (electrical or E-field) signal proportional to the electrical component of electromagnetic signal 1215 and communicates the first signal to antenna port 1270 of first receiver 1225 included in locator 1220 . Locator 1220 also includes a magnetic antenna 1231 that is sensitive to the magnetic component of electromagnetic signal 1215 . Magnetic antenna 1231 detects a second (magnetic or H-field) signal proportional to the magnetic component of electromagnetic signal 1215 and communicates the second signal to second receiver 1227 included in locator 1220 . The second receiver 1227 is constructed substantially similarly to the receiver 1225; to simplify the description of the ranging system 1200, details of the construction of the receiver 1227 are omitted in FIG. 12 .

The exact spacing between the electrical antenna 1232 and the magnetic antenna 1231 is not critical provided the spacing is large enough to avoid unwanted mutual coupling and the spacing is small relative to the wavelength λ of the electromagnetic signal 1215 . The inventors have placed the electric antenna 1232 and the magnetic antenna 1231 apart by a distance on the order of 1%-3% (0.03λ-0.01λ) of a wavelength. In an alternative embodiment, the electric antenna 1232 and the magnetic antenna 1231 may be arranged in a single integral unit having a first terminal producing an E-field response and a second terminal producing an H-field response. Although the spacing between the antennas is preferably small relative to the wavelength λ of the electromagnetic signal 1215, electric antenna 1232 and magnetic Larger spacing between antennas 1231.

Locator 1220 also includes a preselection filter 1242 which receives a first (electrical) signal from antenna port 1270 . The preselection filter 1242 passes first (electrical) signals in the desired frequency band, but rejects signals with unwanted frequencies. Filter 1242 is typically preselected to pass the frequency band in which beacon 1210 transmits electromagnetic signal 1215 for the application of interest. The choice of frequency band will depend on various factors including, but not necessarily limited to, regulatory constraints, propagation behavior of electromagnetic signal 1215, and desired operating distance r. The present invention provides optimal performance for a desired operating distance r limited to approximately 0.08λ to 0.30λ, λ being the wavelength of the electromagnetic signal 1215 emitted by the beacon 1210 . Typical operating distances are usually within 0.05λ to 0.50λ. Higher performance implementations of the invention may operate at distances r of less than 0.05λ or greater than 0.50λ.

Front-end amplifier 1265 increases the amplitude of the first (electrical) signal. If the airborne and other noise is low enough, it is beneficial for the amplifier to have a noise figure low enough to avoid introducing unwanted noise, a dynamic range large enough to accommodate potential changes in the first (electrical) signal amplitude, And the gain is sufficient to produce a first (electrical) signal of suitably large magnitude so that a weak signal will drive the phase detector 1281 properly. The inventors have advantageously used a Mini-Circuits ZFL-500 amplifier as the front-end amplifier 1265, but a variety of other amplifiers are suitable.

A mixer 1252 mixes a first (electrical) signal with a local oscillator signal generated by a local oscillator (LO) 1250 , thereby generating a first intermediate frequency (IF) signal. Local oscillator 1250 may be a conventional sine wave oscillator. Local oscillator 1250 may also be a direct digital synthesizer (DDS), or other waveform template generator. For example, the inventors have used an Analog Devices DDS (AD9835) as the local oscillator 1250, and a Mini-Circuits SBL-3 mixer as the mixer 1252. Various alternative implementations are possible.

IF amplifier 1262 increases the magnitude of the first IF signal. The inventors have found that a pair of current feedback operational amplifiers providing approximately +50dB gain is a suitable embodiment for IF amplifier 1262, but a number of alternatives are available to practitioners in the RF field.

IF filter 1244 accepts only the desired first IF signal and rejects other unwanted signals. A crystal filter can advantageously be used as the IF filter 1244 . Such crystal filters are characterized by an extremely narrow passband and preferably have a constant group delay within the passband. The narrow passband acts to allow the desired first IF representative signal to pass to the phase detector 1281 while rejecting adjacent unwanted signals.

The local oscillator 1250 may also advantageously be used as a tuner to select among the plurality of electromagnetic signals transmitted by the plurality of beacons 1210 . A particular beacon 1210 that emits a particular electromagnetic signal can be distinguished from other beacons that emit other electromagnetic signals having slightly different frequencies. In this way, a single locator 1220 can track many different beacons 1210 . Various other methods for tracking multiple beacons are possible including, for example, time division multiple access, code division multiple access, frequency hopping, or other methods for achieving the desired channelization. Similarly, many different locators 1220 may measure the distance to a particular beacon 1210 . The local oscillator 1250 may be considered a component of an individual receiver 1225 or 1227, or a common frequency standard for multiple receivers 1225,1227.

The phase detector 1281 accepts the first IF signal from the first receiver 1225 and the second IF signal from the second receiver 1227, and produces an output voltage proportional to the phase difference between the first IF signal and the second IF signal . For illustration and not limitation, an exemplary embodiment of phase detector 1281 is Analog Devices AD 8302. This particular phase detector also produces an output proportional to the magnitude difference which can help identify and correct propagation anomalies and in some cases provide more accurate distance determinations.

Range detector 1290 is included in locator 1220 and accepts input from phase detector 1281 for determining the distance r between beacon 1210 and locator 1220 . The inventor implemented the distance detector 1290 using a Measurement Computing Corporation PC-Card-DAS 16/16 A/D PCMCIA Card and a notebook computer, but there are many ways in which a person skilled in the RF arts can implement the distance detector 1290.

The present invention provides good performance for desired operating distances, approximately within a distance r between 0.05λ and 0.50λ, and more desirable performance within a distance r between 0.08λ and 0.30λ, where λ is determined by The wavelength of the electromagnetic signal 1215 emitted by the beacon 1210. Higher performance implementations of the invention may operate at distances r of less than 0.05λ or greater than 0.50λ.

Fixed Beacon-Mobile Locator Structure

13 is a schematic diagram illustrating a near-field ranging system configured according to a fixed beacon-mobile locator architecture. In FIG. 13 , fixed beacon-mobile locator ranging system 1300 includes a first beacon 1310 at a first known fixed location that emits a first electromagnetic signal 1315 . Locator 1320 receives first electromagnetic signal 1315 and determines first distance r ₁ . A second beacon 1312 at a second known fixed location emits a second electromagnetic signal 1317 . Locator 1320 receives second electromagnetic signal 1317 and determines second distance r ₂ . A third beacon 1314 at a third known fixed location emits a third electromagnetic signal 1319 . Locator 1320 receives third electromagnetic signal 1319 and determines third distance _r3 . A fourth beacon 1316 at a fourth known fixed location emits a fourth electromagnetic signal 1321 . The locator 1320 receives the fourth electromagnetic signal 1321 and determines a fourth distance r ₄ . The electromagnetic signals 1315, 1317, 1319, 1321 may be substantially similar electromagnetic signals having substantially similar frequencies, or may be various electromagnetic signals having different frequencies. Electromagnetic signals 1315, 1317, 1319, 1321 may be emitted at substantially the same time or at different times. For example, the beacon 1310 may simultaneously transmit a low frequency signal suitable for long distances and a high frequency signal suitable for short distances. Using the distances r ₁ , r ₂ , r ₃ , r ₄ , the locator 1320 can determine its position. For purposes of illustration and not limitation, four beacons 1310, 1312, 1314, 1316 are illustrated. For some applications a beacon is sufficient to generate useful ranging information. Two beacons produce an indeterminate position in two dimensions, three beacons can produce a definite position in two dimensions, or an indeterminate position in three dimensions, and four beacons can produce a definite position in three dimensions. Using additional beacons to provide distance, one can obtain a more precise location of locator 1320 using multilateral techniques known to those skilled in the RF art.

Locator 1320 may also communicate distance and other useful information via optional data bus 1395 to central controller 1399 for analysis. Central controller 1399 may then relay the position or other information back to locator 1320 via data bus 1395 . A centrally coupled (ie, coupled to all elements of ranging system 1300 ) controller 1399 or locator 1320 may coordinate the operating frequencies or other operating parameters of the locators 1320 and beacons 1310 , 1312 , 1314 , 1316 . Such coordination may include: operating on an appropriate frequency to avoid interference or to obtain optimal distance information. Coordination can also include scheduling the time or duty cycle of operations. Coordination may also include transmit power control for coexistence, signal security, or other reasons.

The fixed beacon-mobile locator system 1300 is advantageous when one wishes to track a limited number of assets, or if one wishes to have position, location, navigation or guidance information available at potentially many mobile locations. Fixed beacon-mobile locator system 1300 is adapted to provide users (with locator 1320) with rapid updates of location within an area around or throughout which multiple beacons (e.g., beacons 1310, 1312, 1314, 1316) have been deployed ). Various applications are possible. For purposes of illustration and not limitation, several applications are listed below.

For example, fixed beacons 1310, 1312, 1314, 1316 may be deployed on or around golf courses, lawns, farms, or other areas where precise guidance of devices is desired. Positioner 1320 may be placed on a robotic tractor, lawn mower, golf ball collector, harvester, fertilizer spreader, or other equipment. Locator 1320 may be used in guidance or navigation systems for such devices. Locator 1320 may also be used to track golf carts or other assets. Locator 1320 may be used to assist golfers or others in determining their location, particularly their location relative to a golf hole or other landmark of interest.

Stationary beacons 1310, 1312, 1314, 1316 can be used in shopping malls, stores, museums, businesses, amusement parks, urban areas, parks, suburbs, seaports, lakes, real estate, homes where people would like someone or device to be able to monitor their location or location. , residential units, or other areas or equipment in or around them. Locator 1320 may be carried by an individual so that the individual can monitor his or her own location or that of another person such as a family member, friend, or other person of interest. Locator 1320 may also be carried by an individual so that the individual can determine their location relative to a landmark or other point or points of interest. Locator 1320 may be incorporated into a device that provides the user with location-specific information, such as prices or other information about nearby objects for sale, appraisal, or valuation. Locator 1320 may also be incorporated into a device that provides the user with location-specific information describing nearby attractions, shows, exhibits, adventures, or other features that may be of interest.

A locator 1320 may be incorporated into the vehicle to provide position, guidance or navigation information. Examples are precision guidance or navigation systems for aircraft such as Unmanned Aerial Vehicles (UAVs), boats, cars, Unmanned Ground Vehicles (UGVs) or other vehicles.

Fixed/Mobile Locator-Mobile Beacon Structure

14 is a schematic diagram illustrating a near-field ranging system configured according to a fixed/mobile locator-mobile beacon structure. In Figure 14, a fixed/mobile locator-mobile beacon ranging system 1400 includes a mobile beacon 1410 that transmits a first electromagnetic signal 1415, a second electromagnetic signal 1417, a third electromagnetic signal 1419, a fourth electromagnetic signal 1421 and a first electromagnetic signal 1415. Five Electromagnetic Signals 1423. The electromagnetic signals 1415, 1417, 1419, 1421, 1423 may be substantially similar electromagnetic signals having substantially similar frequencies, or multiple electromagnetic signals having different frequencies. Electromagnetic signals 1415, 1417, 1419, 1421, 1423 may be transmitted at substantially the same time or at different times. For example, the mobile beacon 1410 may simultaneously transmit a low frequency signal suitable for a long distance and a high frequency signal suitable for a short distance.

The first fixed locator 1420 receives the first electromagnetic signal 1415 and determines a first distance r ₁ . The second fixed locator 1422 receives the second electromagnetic signal 1417 and determines a second distance r ₂ . Third fixed locator 1424 receives third electromagnetic signal 1419 and determines third distance r ₃ . The fourth fixed locator 1426 receives the fourth electromagnetic signal 1421 and determines a fourth distance r ₄ . Fifth mobile locator 1428 receives fifth electromagnetic signal 1423 and determines fifth distance r ₅ . For purposes of illustration, fifth mobile locator 1428 is shown as an directional locator of the type described as directional locator 1020 (FIG. ) of the type of omnidirectional locator described.

For purposes of explanation and not limitation, four fixed locators 1420 , 1422 , 1424 , 1426 and one mobile locator 1428 are illustrated in FIG. 14 . A single locator is sufficient to generate useful distance information for some applications. For example, a single mobile locator 1428 may enable a user to determine the distance r ₅ to the mobile beacon 1410 , thus allowing the user to target the mobile beacon 1410 . Two locators produce an indeterminate position in two dimensions, three locators can produce an unambiguous position in two dimensions, or an indeterminate position in three dimensions, and four locators produce an unambiguous position in three dimensions. Using additional beacons to provide distance, one can obtain a more precise position of beacon 1410 using multilateral techniques known to those skilled in the RF art

When the distance measuring system 1400 includes a data bus 1495, the locators 1420, 1422, 1424, 1426, 1428 can transmit the distance r ₁ , r ₂ , r ₃ , r ₄ , r ₅ to the central controller 1499 or Another device (not shown in Figure 14) connected to data bus 1495. The central controller 1499 can collect the distances r ₁ , r ₂ , r ₃ , r ₄ , r ₅ , calculate the position of the beacon 1410 , and relay that position information to any other device connected to the data bus 1495 .

Central controller 1499 (or another device connected to data bus 1495 ) may coordinate the operating frequency or other operating parameters of mobile beacons 1410 and locators 1420 , 1422 , 1424 , 1426 , 1428 . Such coordination may include: operating on an appropriate frequency to avoid interference or to obtain optimal distance information. Coordination can also include scheduling the time or duty cycle of operations. Coordination may also include transmit power control for coexistence, signal security, or other reasons.

Ranging system 1400 is particularly well configured for tracking a large number of assets including, for example, tracking people or assets from a central location. Various applications are possible. For purposes of illustration and not limitation, several applications are listed below.

For example, multiple fixed locators (e.g., locators 1420, 1422, 1424, 1426) may be deployed in or around a particular area of interest where one wishes to track multiple beacons attached to assets of interest (eg, beacon 1410). The ranging system 1400 is ideal for tracking automobiles, rental equipment, parts, components, tools, or other assets in manufacturing facilities, retail locations, warehouses, cargo bays, vehicles, cargo, containers, storage areas, hospitals, or other areas where one wishes to track asset equipment. Individual mobile beacons 1410 may be placed in each car, each piece of leased equipment, part, component, tool, or other asset whose location is desired to be known. Mobile locators (e.g., mobile locator 1428) may be used to help identify roaming mobile beacons 1410 if each mobile beacon 1410 moves away from an area in or around which fixed locator installations have been deployed. s position. This functionality is especially useful if a roaming mobile beacon 1410 is connected to stolen property. A locator, such as locator 1420, may be associated with a traffic signal, toll booth, or other traffic-related facility, and may monitor each moving beacon 1410 in an approaching emergency vehicle, bus, or car, thus allowing traffic signal tracking. Monitoring of precision control or other conditions. Here it is useful to remember that the electromagnetic signal associated with the ranging system 1400 can be modulated to contain information, such as identification information about the asset, the asset to which the mobile beacon is attached. In this manner, various assets carrying each mobile beacon 1410 may be individually identified or authenticated within ranging system 1400 .

Additionally, multiple fixed locators (e.g., locators 1420, 1422, 1424, 1426) may be deployed in or around particular areas of interest where one wishes to track multiple Beacons for (eg, Beacon 1410). As such, the ranging system 1400 is well suited for tracking emergency responders such as fire, police, SWAT team members and medical personnel at the scene of an incident. Ranging system 1400 may be used to track employees in hazardous environments, such as miners in mines, workers at equipment where hazardous materials are present, or correctional officers or prisoners in prisons. Ranging system 1400 may also be used to track patients, physicians, or other vital personnel or equipment in a hospital, nursing home, or other structure.

In another illustrative example, ranging system 1400 may track skiers in a ski area, making it easy to locate the skiers even in the event of an avalanche or other emergency. Similar applications include tracking hikers, climbers, gliders, hunters, anglers, outdoorsmen and others who are engaged in potentially dangerous activities and may need rescue or assistance.

Patrons can be tracked at amusement parks, museums, festivals, sporting events, conventions, conferences or other dense crowds. The location of players in sports games such as football players, football players, baseball players, swimmers, runners and other sports participants may be monitored to aid in the refereeing, reporting or analysis of sports games. Sports equipment or animals may be tracked, including: for illustration and not for limitation, soccer, baseball, soccer, rugby, racing cars, rowing boats, thoroughbreds or clipper boats.

Essential personnel can be located in a store or facility. Monitor children and others requiring supervision around your home, neighborhood, school, campus, or other facility. The ranging system 1400 can also be applied to a Personal Emergency Response System (PERS) to allow rescuers to quickly locate a person in need, such as a patient who has been lost from a nursing home. Inmates may be tracked as part of a release home or other low security supervision program. Persons whose actions are subject to restraining orders or other restrictions may be monitored to deter them from violating the restrictions. Mobile locators (e.g., mobile locators 1428) may be used to help spot people who have left areas in or around which fixed locators (e.g., fixed locators 1420, 1422, 1424, 1426) have been placed. facility.

The ranging system 1400 can also be used to track pets as part of a pet containment system, or to allow the owner to monitor the pet's location. Wildlife may be tracked as part of a conservation project, research effort, or for other reasons. Ranging system 1400 may also be used to track and monitor livestock or other domesticated animals.

Interactive beacon-locator

15 is a schematic diagram illustrating a near-field ranging system configured according to an interactive beacon-locator architecture. In FIG. 15 , an interactive beacon-locator structure 1500 includes a first beacon-locator 1520 and a second beacon-locator 1522 . The first beacon-locator 1520 transmits the first electromagnetic signal 1515 . The second beacon-locator 1522 receives the first electromagnetic signal 1515 and calculates the distance r to the first beacon-locator 1520 . Second beacon-locator 1522 may also emit second electromagnetic signal 1517 . The first beacon-locator 1520 receives the second electromagnetic signal 1517 and calculates the distance r. If first beacon-locator 1520 and second beacon-locator 1522 are connected by optional data bus 1595, first beacon-locator 1520 can trigger second beacon-locator 1522 to send a second electromagnetic signal 1517 so that the first beacon-locator 1520 can determine the distance r. For illustration and not limitation, only two beacon-locators are shown. But in some applications it is advantageous to have additional beacon-locators so that each member of a larger group can be tracked or be tracked.

Various applications are suitable for ranging system 1500 . For illustration and not limitation, several applications are listed below. Interactive beacon-locator 1500 is useful in conjunction with two-way radios whose users wish to know how far away communicating parties are. One can also advantageously incorporate beacon-locators 1520, 1522 into devices that allow people to discover each other or other devices where consolidated tracking and communication within a group or between members of a group is desired, allowing people to discover each other's Equipment such as parents and children in amusement parks, hunters, anglers, or other people who are active in the wild. Such a combined tracking and communication arrangement may be useful not only for people, but also for vehicles, especially aircraft and ships that need to maintain a certain separation or position within a moving group. If the means for orientation is also used in special applications, distance and azimuth information can be obtained. The interactive beacon-locator 1500 is also useful for allowing members of a team to monitor each other's locations when visibility is impaired by smoke or other intervening walls or objects. Additionally, interactive beacon-locator 1500 may be advantageously used as part of a communication security system that uses distance or location information to verify or verify the identity of communicating parties.

passive tag structure

16 is a schematic diagram illustrating a near-field ranging system configured using a passive tag structure. In FIG. 16 , a passive tag ranging system 1600 includes a locator 1620 equipped with an interrogator antenna 1638 that radiates an interrogating electromagnetic signal 1616 . In alternative embodiments, the function of the interrogator antenna 1638 may be performed by the first magnetic antenna 1631 , the second magnetic antenna 1633 or the electrical antenna 1632 . Interrogation electromagnetic signal 1616 is detected by interrogator antenna 1639 of passive tag 1629 . Passive tag 1629 from. The interrogating electromagnetic signal 1616 harvests energy and re-radiates the harvested energy as an electromagnetic signal 1617 through the passive tag transmit antenna 1635 .

The interrogating electromagnetic signal 1616 and the re-radiated electromagnetic signal 1617 may have different frequencies or other different properties. Although the interrogator antenna 1639 and the passive tag transmit antenna 1635 are shown as magnetic antennas, they may be implemented in electrical antennas. Additionally, passive tag 1629 includes an active device that modulates re-radiated electromagnetic signal 1617 . Electromagnetic signal 1617 is detected by first magnetic antenna 1631 , second magnetic antenna 1633 and electric antenna 1632 . The locator 1620 then uses the near-field distance measurement teachings of the present invention to determine the distance r to the passive tag 1629, and possibly the direction as well.

Passive tag ranging system 1600 is a good product solution when low cost but high capacity implementation is an important objective. Passive tags 1629 may be attached to luggage, mail, assets for inventory control or theft prevention, identification cards or other personal artifacts, or multiple other persons or assets whose location is desired to be known with high precision.

Multiple adjacent passive tags 1629 may be distinguished from one another by responding to different interrogating electromagnetic signals 1616, or by various modulations applied to each emitted electromagnetic signal 1617.

Near Field Remote Sensing Structure

17 is a schematic diagram illustrating a near-field ranging system configured using a near-field remote sensing structure. In FIG. 17 , a near-field remote inductive ranging system 1700 includes a remote near-field sensor 1720 equipped with an interrogator antenna 1738 that radiates an interrogating electromagnetic signal 1716 . In alternative embodiments, the function of the interrogator antenna 1738 may be performed by the first magnetic antenna 1731 , the second magnetic antenna 1733 or the electrical antenna 1732 . Interrogating electromagnetic signal 1716 is incident on remotely sensed object 1719 . When incident interrogating electromagnetic signal 1716 is reflected from remotely sensed object 1719, reflected electromagnetic signal 1717 is generated. The nature of the reflected electromagnetic signal 1717 depends on the electrical and geometric properties of the remotely sensed object 1719 , as well as on the distance r between the near field sensor 1720 and the remotely sensed object 1719 . The reflected electromagnetic signal 1717 is detected by the first magnetic antenna 1731 , the second magnetic antenna 1733 or the electric antenna 1732 . Near-field sensors 1720 may evaluate reflected electromagnetic signals 1717 to infer properties of remotely sensed objects 1719 .

Near Field Ranging Method

Figure 18 is a flowchart illustrating the method of the present invention. Method 1800 for measuring a distance between a first location and a second location begins at START block 1802 . As represented by block 1804, method 1800 continuously transmits electromagnetic signals from a first location. Method 1800 continues to receive electromagnetic waves at a second location; the second location is within a near-field range of the electromagnetic signal, as indicated by block 1806 . Method 1800 proceeds sequentially, in no particular order: (1) detecting a first characteristic of the electromagnetic signal, as indicated by block 1808 ; and (2) detecting a second characteristic of the electromagnetic signal, as indicated by block 1810 . As indicated by block 1812, method 1800 continuously measures the difference between the first feature and the second feature. As indicated by block 1814 , method 1800 continues to utilize the measured difference represented by block 1812 to calculate the distance between the first location and the second location. As indicated by an end (END) block 1816, the method 1800 ends.

For purposes of illustration and not limitation, fixed beacon-mobile locator ranging system 1300 (FIG. 13), fixed/mobile locator-mobile beacon ranging system 1400 (FIG. 14), interactive beacon- Locator ranging system 1500 (FIG. 15), passive tag ranging system 1600 (FIG. 16), and near-field remote sensing ranging system 1700 (FIG. 17). Various alternative configurations and combinations of structures are also possible. For example, fixed locators 1420, 1422, 1424, 1426 (FIG. 14) may be implemented in a beacon-locator configuration, such as beacon-locator 1520 (FIG. 15). Fixed locators 1420, 1422, 1424, 1426 (FIG. 14) may be configured to cooperatively measure their own respective positions on their own to enable rapid deployment of position determining, positioning or tracking systems. The provision of specific exemplary applications in connection with the configurations of the ranging systems described herein should not be construed as excluding applications of different configurations for a given exemplary application.

In another example, passive tags 1629 (FIG. 16) may be used with a network of locators (eg, fixed locators 1420, 1422, 1424, 1426; FIG. 14). Additionally, nothing in this disclosure should be construed to preclude ranging, positioning, or positioning systems from using additional information to refine an estimate of position. Other information used may include, by way of example and not limitation, a history of past positions or changes in position, or information from other sensors or sources. In particular, the invention is well suited as a complement to GPS type tracking systems. The present invention can extend the functionality of a GPS type tracking and positioning system to areas where GPS signals are impenetrable or unavailable. Furthermore, the present invention can also be used to achieve a level of performance not achievable with GPS alone. Nothing in this disclosure should be construed as precluding use of the present invention in conjunction with any other prior art techniques for tracking, determining position or positioning. Similarly, the present invention can be supplemented with prior art systems to improve the performance of the present invention in areas or distances where the present invention alone does not produce reliable results.

Although, for simplicity, the present disclosure focuses on a single polarization in explaining the present invention, it should be understood that the teachings of the present invention can be easily extended to multi-polarization or polarization-different systems with multiple parallel receive channels, including the use of Circularly polarized systems. Various polarization capabilities allow the system taught by the present invention to accommodate various orientations between beacon or passive tags and locators.

To aid in understanding the invention, this disclosure focuses on a narrowband continuous wave (CW) implementation of the invention. It should be understood that multiple frequencies, time-domain impulse waveforms, collections of appropriate frequency steps or sweeps, or other signals more complex than a single narrowband CW signal may also be used to practice the invention. For example, the phase difference of a CW signal may involve a time delay, or more generally, a Hilbert transform of an arbitrary signal. Any waveform (whether a CW waveform, a short pulse, a shock, or a time domain waveform, a sharp waveform, or other waveform) will develop from a near-field shape to a long-range shape in a manner that enables distance measurements and Convenient location.

Specific applications are provided for purposes of illustration only, to assist the reader in understanding a few of the many environments in which the invention will prove useful. It should also be understood that while the detailed drawings and specific examples are given to describe preferred embodiments of the invention, they are for purposes of illustration only and the inventive apparatus and methods are not limited to the precise details and conditions disclosed, and wherein Various changes may be made without departing from the spirit of the invention as defined in the appended claims.

Claims (18)

1. A system for measuring the distance between a first location and a second location, the system comprising: (a) a beacon device positioned at said first location and emitting an electromagnetic signal; and (b) a locator device positioned at said second location and receiving said electromagnetic signal, wherein said locator device is positioned at a distance from said beacon device within a near-field range of said electromagnetic signal; said locator device differentiates between said electromagnetic signal sensed at said second location at least two features; and said locator device utilizes said at least two features to achieve said measurement. 2. The system for measuring the distance between a first location and a second location according to claim 1, wherein said at least two characteristics are: a first signal characteristic proportional to a magnetic field component of said electromagnetic signal, and a second signal characteristic proportional to the electric field component of said electromagnetic signal. 3. The system for measuring the distance between a first location and a second location according to claim 2, wherein said locator device measures the distance between said magnetic field component and said electric field component of said electromagnetic signal The measurement is carried out by using the phase difference and determining the distance using the phase difference. 4. The system for measuring the distance between a first location and a second location of claim 1, wherein the beacon device and the locator device are coupled in a single package. 5. The system for measuring the distance between a first location and a second location of claim 2, wherein the beacon device and the locator device are coupled in a single package. 6. The system for measuring the distance between a first location and a second location according to claim 1, wherein said beacon device transmits said electromagnetic signal in response to receiving an interrogation signal from said locator device . 7. The system for measuring the distance between a first location and a second location according to claim 1, wherein said system comprises at least one additional locator device to include at least n locator devices in the system, so The at least n locator devices measure the beacon device, so as to ascertain the position of the beacon device in n dimensions. 8. The system for measuring the distance between a first location and a second location according to claim 4, wherein said at least two characteristics are: a first signal characteristic proportional to a magnetic field component of said electromagnetic signal, and a second signal characteristic proportional to the electric field component of the electromagnetic signal; the locator device implements the Measurement. 9. The system for measuring the distance between a first location and a second location according to claim 6, wherein said at least two characteristics are: a first signal characteristic proportional to a magnetic field component of said electromagnetic signal, and a second signal characteristic proportional to the electric field component of the electromagnetic signal; the locator device implements the Measurement. 10. The system for measuring the distance between a first location and a second location according to claim 7, wherein said at least two characteristics are: a first signal characteristic proportional to a magnetic field component of said electromagnetic signal, and a second signal characteristic proportional to the electric field component of the electromagnetic signal; each corresponding locator device in the at least n locator devices measures the phase difference between the magnetic field component and the electric field component and utilizes The phase difference determines the distance to effectuate the measurement. 11. A device for realizing electromagnetic ranging, said device comprising: (a) Transmitter equipment for emitting electromagnetic waves; (b) a receiver device for receiving said electromagnetic waves, wherein said receiver device is positioned at a distance from said beacon device within a near-field range of said electromagnetic signal; said receiver device comprising: first receiver means for detecting a first characteristic of said electromagnetic waves, and second receiver means substantially juxtaposed with said first receiver means for detecting a second characteristic of said electromagnetic waves; (c) a measurement device coupled to said receiver device for measuring a difference between said first characteristic and said second characteristic; and (d) a determining device coupled to said measuring device for computing said distance using said difference. 12. The apparatus for realizing electromagnetic ranging according to claim 11, wherein said first characteristic is a first signal characteristic proportional to the magnetic field component of said electromagnetic wave, and said second characteristic is a characteristic proportional to said The electric field component of the electromagnetic wave is proportional to the second signal characteristic; the difference is a phase difference between the magnetic field component and the electric field component; and the determining means calculates the distance using the phase difference. 13. The apparatus for implementing electromagnetic ranging according to claim 11, wherein said transmitter device transmits said electromagnetic waves in response to receiving an interrogation signal from said receiver device. 14. The apparatus for realizing electromagnetic ranging according to claim 13, wherein said first characteristic is a first signal characteristic proportional to the magnetic field component of said electromagnetic wave, and said second characteristic is a characteristic proportional to said An electric field component of the electromagnetic wave is proportional to a second signal characteristic; said difference is a phase difference between said magnetic field component and said electric field component; and said determining means uses said phase difference to calculate said distance. 15. A method for measuring the distance between a first location and a second location, said method comprising the steps of: (a) emitting electromagnetic waves from said first location; (b) receiving said electromagnetic wave at said second location, wherein said second location is within a near-field distance of said electromagnetic wave; (c) In no particular order: (1) detecting a first characteristic of the electromagnetic wave at the second location; and (2) detecting a second characteristic of the electromagnetic wave at the second location; (d) measuring a difference between said first feature and said second feature at a second location; and (e) Computing the distance using the difference. 16. The method for measuring the distance between a first location and a second location according to claim 15, wherein said first characteristic is a first signal characteristic proportional to a magnetic field component of said electromagnetic wave, and said The second characteristic is a second signal characteristic proportional to the electric field component of the electromagnetic wave; and the difference is a phase difference between the magnetic field component and the electric field component. 17. The method for measuring the distance between a first location and a second location according to claim 15, wherein said emitting said electromagnetic wave occurs in response to receiving an interrogation signal. 18. The method for measuring the distance between a first location and a second location according to claim 17, wherein said first characteristic is a first signal characteristic proportional to a magnetic field component of said electromagnetic wave, and said The second characteristic is a second signal characteristic proportional to the electric field component of the electromagnetic wave; and the difference is a phase difference between the magnetic field component and the electric field component.

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