JPH10135760A - Polarized filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance polarized filter by eliminating interference between resonance circuits and between a resonance circuit and a coupling inductor. SOLUTION: In the polarized filter having 1st, 2nd and 3rd resonance circuits that have attenuation pole frequencies fp1, fp2, fp3 in the order of frequency closer to the cut-off frequency fc, two coil insert holes 12, 13 are made to a dielectric multi-layer board 11, earth patterns 14, 19 are formed around openings 12a, 13a of the coil insert holes 12, 13 except part, pads 16, 17, 21 are formed to the part at which no earth patterns 14, 19 are formed, and the 1st and 2nd resonance circuits whose attenuation pole frequencies are respectively fp1, fp2 are inserted to the coil insert hole 12 and the 3rd resonance circuits whose attenuation pole frequency is fp3 is inserted to the coil insert hole 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polar filter comprising a lumped constant element and a distributed constant element, and more particularly to a polar filter suitable for use as an antenna duplexer used in mobile communication equipment. is there.

[0002]

2. Description of the Related Art In mobile communication equipment, a polar filter is used as an antenna duplexer for switching between a reception system and a transmission system. In this polarized filter,
Conventionally, coupling between the resonators is performed by a capacitor and a coil. A resonator constituent material is mainly used as the coupling capacitance or the coupling coil.

[0003]

However, when this polarized filter is formed on a multilayer substrate having a limited area, interference between resonators and between the resonator and the coupling material are caused by interference. This has been a major obstacle when steep attenuation characteristics are required.

[0004]

A polarized filter according to the present invention is a polarized filter comprising a lumped constant element and a distributed constant element.
First, second, and third with attenuation pole frequencies of fp2 and fp3
And the second resonance circuit and the third resonance circuit are separated from each other and arranged on a multilayer substrate.

In the polarized filter having the above configuration, the second type
By arranging the resonance circuit and the third resonance circuit separately on the multilayer substrate, interference between the resonance circuits and between the resonance circuit and the coupling inductor is eliminated. As a result, the performance of the frequency characteristics of the polarized filter is improved.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing an equivalent circuit of a transmission filter in a polar filter used as an antenna duplexer used in, for example, mobile communication equipment. FIG.
, Input terminals a1, a2, output terminals b1, b2,
The coupling inductors L1, L3, L5, L7 connected in series between the input terminal a1 and the output terminal b1, and each connection point P of the coupling inductors L1, L3, L5, L7
A transmission filter is formed by the series resonance circuits 1, 2, and 3 connected between the input / output terminals a2 and b2 and the input / output terminals a2 and b2.

In this transmission filter, the resonance circuit 1
Is represented by a capacitor (lumped constant element) C2 and a coil (distributed constant element) L2 connected in series, and the resonance circuit 2 is composed of a capacitor C4 and a coil L4 connected in series.
The resonance circuit 3 includes a capacitor C6 and a coil L6 connected in series. Here, each attenuation pole frequency fp1, fp2,
fp3 is set to fp1, f in order from the one closer to the cutoff frequency fc.
p2 and fp3.

In the frequency characteristics of this filter, the order of the resonance circuits having a small insertion loss in the band is fp2, fp
1, fp3. Here, the insertion loss is a value that gives a result generated by inserting a resonance circuit, and the power that is given to a certain place after the resonance circuit and the power that is given to the same place when the resonance circuit is removed. Is expressed in decibels.

In order to arrange the resonance circuits of the attenuation pole frequencies fp1, fp2, fp3 on a multilayer substrate having a limited area, as shown in FIG.
, Are arranged in a horizontal line to shield them collectively, as shown in FIG. 3B, a method of combining a resonance circuit and a resonance circuit, and separately shielding the resonance circuit, and FIG. As shown in c), a method of combining a resonance circuit and a resonance circuit and separately shielding the resonance circuit from the resonance circuit can be considered. Table 1 shows the frequency characteristics of the antenna duplexer in these arrangements.

[0011]

[Table 1]

As is apparent from Table 1, FIG.
Only in the case of the above, interference occurs between the resonance circuits and between the resonance circuit and the coupling inductor, and fp1 and fp2
And the attenuation poles of fp3 and fp3 are not close to each other, and accordingly, a phenomenon occurs in which the performance of the frequency characteristics of the polar filter is deteriorated. Therefore, when the resonance circuits of the attenuation pole frequencies fp1, fp2, and fp3 are arranged on a multilayer substrate having a limited area, the arrangement method shown in FIGS. A polarized filter can be realized.

FIG. 4 is a circuit diagram showing an equivalent circuit when the equivalent circuit of FIG. 2 is realized on a multilayer substrate. When realized on a multilayer substrate, the connection between the chip capacitor C and the coil L of the resonance circuit needs to be through a pad (PAD).
In FIG. 4, PAD1, PAD2, and PAD3 are used for the respective resonance circuits of the attenuation pole frequencies fp1, fp2, and fp3.

FIG. 1 is a schematic plan view showing an embodiment of the present invention, and shows an actual mounting structure when, for example, the arrangement method shown in FIG. 3B is used. In FIG. 1, a dielectric multilayer substrate 1 made of, for example, FR-4 or a polyimide material
1, a coil insertion hole 12 having an elongated opening 12a along one long side thereof and penetrating from the upper surface to the lower surface of the substrate 11 is formed. A coil insertion hole 13 having a shorter opening 13a and also penetrating from the upper surface to the lower surface of the substrate 11 is formed.

A ground pattern 14 is formed around the opening 12a of the coil insertion hole 12 except for a part of the opening 12a.
1 are arranged on the upper and lower surfaces. The ground patterns 14 on the upper and lower surfaces are connected by through holes 15 and function as a shield material. Two pads 16 and 17 are provided in a portion where the ground pattern 14 is removed with a short ground pattern 14a interposed therebetween. In addition, these pads 1
Through holes 18 are formed on both sides of the multilayer substrate 11 from the upper surface to the lower surface of the multilayer substrate 11.

Similarly, ground patterns 19 are arranged on the upper and lower surfaces of the multilayer substrate 11 around the opening 13a of the coil insertion hole 13 except for a part thereof. The ground patterns 19 on the upper and lower surfaces are connected by through holes 20,
Acts as a shielding material. Pads 21 are provided in portions where the ground pattern 19 is removed. Further, on both sides of the pad 21, through holes 22 extending from the upper surface to the lower surface of the multilayer substrate 11 are formed.

Here, when the arrangement method of the resonance circuit shown in FIG. 3B is adopted, the resonance circuit,
However, a resonance circuit is inserted into each of the coil insertion holes 13. As these resonance circuits, an air-core coil, for example, a multilayer board coil 30 shown in FIG. 5 is used. Hereinafter, the configuration of the multilayer substrate coil 30 will be described.

In FIG. 5, an input / output pad 32 is formed on a dielectric multilayer substrate 31, and a microstrip line 33 corresponding to a coil wire is formed over each layer. The microstrip line 3 of each of these layers
3 form a coil by being connected by a through hole 34. Further, an earth pattern 35 is arranged on the periphery of the multilayer substrate 31.

A capacitor 36 is externally connected between the input / output pad 32 and the beginning of the microstrip line 33 to form a resonance circuit. The end of the microstrip line 33 is connected to the ground pattern 35 to form a short-circuit line.

The multilayer substrate coil having such a configuration becomes an air-core coil by interposing a dielectric between the microstrip lines 33 of each layer. Here, in consideration of the capacitance of the pad 32 (the dielectric constant and Q of the substrate material), as shown in FIG. 6, the pad capacitance C0 is parallel to the coil L0 with respect to the reference circuit (a) of the LC series resonance circuit. Connected circuit (b)
Becomes

As described above, when the resonance circuit of the polarized filter is formed on a multilayer substrate, the pad capacitance changes depending on the distance from the ground (earth pattern), so it is necessary to consider the effect of the pad capacitance. There is. Here, the relationship between the Q value of the resonance circuit and the pad capacitance will be considered.

First, in the reference circuit shown in FIG. 6A, as preconditions: (1) Reference element L1 = 100 nH, C1 = 0.357
pF (2) Resonance frequency fp = 869 MHz (3) Polar attenuation αp = 30 at fp = 869 MHz
dB (4) C1 is lossless, and the resistance component r due to the Q value of L1 is
From r = ωL / Q, r = 0.015811, and the Q value in this case is Q = 691.

Based on these preconditions, the circuit shown in FIG. In this circuit, the self-resonant frequency of the coil L0 is f10, and the equivalent L value of this circuit is L1.
Assuming 0, each is given by: f10 = 1 / {2 · π · (L0 · C0) ^1/2 } (1) L10 = L0 {1− (fp / f10) ² } (2)

Here, the Q value of the pad capacitance C0 is Q = 20.
6 when Q = 40 and when FR-4 is used as the substrate material when the pad capacitance C0 changes.
Table 2 shows the relationship between the resonance circuit of FIG.

[0025]

[Table 2]

As is apparent from Table 2, the resonance characteristics are affected by the pad capacitance C0 and its Q value.
When the pad capacitance C0 increases by about 0.01 pF near = 600, Q0 fluctuates by about 100, and the deterioration of the resonance characteristics appears remarkably.

Therefore, in order to reduce the pad capacitance C0 of the resonance circuit on the multilayer substrate 11, as shown in FIG.
In the multilayer substrate 11, through holes 18, 22 may be formed between the pads 16, 17, 22 and the ground patterns 14, 19, or the substrate may be penetrated. Pad 16,1
7 and 22 and ground patterns 14 and 19
Table 3 shows the measurement results when holes 8 and 22 were drilled.

[0028]

[Table 3]

As is clear from Table 3, the multilayer substrate 1
1, the through holes 18, 22 are formed in the pads 16, 17, 22.
By piercing between the ground pattern and the ground patterns 14 and 19, the pad capacitance C0 can be reduced by about 0.03 pF. As described above, by reducing the pad capacitance C0, the performance of the resonance circuit on the multilayer substrate is improved, and accordingly, the performance of the polarized filter can be improved.

[0030]

As described above, according to the present invention,
It has first, second, and third resonance circuits having attenuation pole frequencies of fp1, fp2, and fp3 from the one closer to the cutoff frequency, and the second resonance circuit and the third resonance circuit are separated from each other to form a multilayer substrate. With the arrangement above, interference between the resonance circuits and between the resonance circuit and the coupling inductor is eliminated, so that a high-performance polarized filter can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of a transmission filter.

FIG. 3 is a diagram illustrating an example of an arrangement position of a resonance circuit.

FIG. 4 is a circuit diagram showing an equivalent circuit when realized on a multilayer substrate.

FIG. 5 is a schematic perspective view of a multilayer substrate coil.

FIG. 6 is a circuit diagram showing an equivalent circuit of the resonance circuit.

[Explanation of symbols]

 1,2,3 Resonant circuit 11,31 Dielectric multilayer substrate 12,13 Coil insertion hole 14,19,35 Ground pattern 16,17,21,32 Pad 18,22 Through hole 30 Multilayer substrate coil 33 Microstrip line

Claims (4)

[Claims] 1. A polarized filter comprising a lumped-constant element and a distributed-constant element, wherein said first, second, and third resonance circuits have attenuation pole frequencies of fp1, fp2, and fp3 from a frequency closer to a cutoff frequency. A polar filter comprising: the second resonance circuit and the third resonance circuit being separated from each other and arranged on a multilayer substrate. 2. The polarized filter according to claim 1, wherein the first, second, and third resonance circuits are configured using an air-core coil. 3. The polarized filter according to claim 2, wherein said air core coil is a multilayer substrate coil. 4. The multi-layer substrate according to claim 1, wherein said first, second, third
Insertion hole into which the resonance circuit is inserted, a ground pattern formed by removing a part around the insertion hole, a pad formed in a portion where the ground pattern is removed, the pad and the ground pattern The polar filter according to claim 1, 2 or 3, further comprising a through-hole formed between the filter and the filter.