JPH08274504A - Filter device for high frequency - Google Patents

Abstract

PURPOSE: To provide more ideal filter characteristics while miniaturizing and lightening the parts. CONSTITUTION: An LPF 36 is composed of a coil 10 and a capacitor 18 at the input side and with this LPF, unwanted high frequency components are removed. A first stage trap circuit 38 is composed of a capacitor 20 and a resonator 22 on the following stage, and a second stage trap circuit 40 is composed of a capacitor 28 and a resonator 30. At these trap circuits 38 and 40, unwanted low frequency components are respectively removed by the serial resonance of the capacitor 20 and an equivalent inductance 24 and the serial resonance of the capacitor 28 and an equivalent inductance 32. Since the Q of a resonator trap is higher than that of an LC trap, much sharper and more ideal attenuation characteristics can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an HPF (High Pass Filter) and LPF in a high frequency band such as microwaves.
The present invention relates to a filter device such as a (Low Pass Filter) and a BPF (Band Pass Filter), and more specifically to a high frequency filter device using a dielectric resonator or a stripline resonator.

[0002]

BACKGROUND ART As a filter device in a high frequency band such as a microwave, there is one shown in FIG. 10 (A), for example. In this filter device, BPFs are connected in two stages. Capacitors 900, 902, 904 are connected to the input terminal T1 and the output terminal T2.
Are connected in series, and a capacitor 906 for trapping is connected in parallel to the capacitors 900 and 902. In addition, the output side of the capacitors 900 and 902 and the GND
Dielectric resonators 908 and 910 are connected to (ground), respectively. The capacitor 900 and the dielectric resonator 908 form a first-stage BPF, and the capacitor 902 and the dielectric resonator 910 form a second-stage BPF.

FIGS. 3B and 3C show the measured frequency characteristics of the prototype filter device. The same figure (B) shows the characteristics of the passing wave and (C) shows the characteristics of the reflected wave. As shown in these figures, the pass band is around 1.8 to 2 GHz. The peak P1 on the low frequency side is formed by the capacitor 906.

On the other hand, even in the microwave band filter device, the size of the filter device has been reduced recently as seen in mobile phones and the like.
The demand for weight reduction is remarkable, and it is required to satisfy these demands. However, there is a limit in obtaining steeper and ideal filter characteristics while satisfying such a demand by the conventional method.

The present invention focuses on these points, and an object thereof is to obtain more ideal filter characteristics while reducing the size and weight of parts. Another purpose is to reduce the number of elements that make up the circuit to reduce costs,
It is to reduce loss.

[0006]

In order to achieve the above-mentioned object, the present invention is to connect a capacitor or a coil in series to a resonator constituted by a dielectric or a strip line, and the capacitors or coils are connected to each other by an equivalent inductance or It is characterized in that a resonator trap configured to generate an equivalent capacitance and series resonance at a desired frequency is connected to a filter circuit. Resonator trap is L
Since the Q is higher than that of the C trap, a steeper and ideal attenuation characteristic can be obtained. The above and other objects, features and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS While there may be many embodiments of the present invention, a suitable number of embodiments will now be shown and described in detail.

<First Embodiment> First, a first embodiment will be described with reference to FIGS. FIG. 1 shows the first embodiment.
BPF filter device is shown with input terminal TA
Between the output terminal TB and the capacitor 10, 12, 14
Are connected in series in that order. Input terminals TA and GN
A capacitor 16 and a resonator 18 are connected to D in series. A parallel circuit of an inductance 22 and a capacitance 24 is connected to the output side of the capacitor 10 and GND. Further, a parallel circuit of an inductance 26 and a capacitance 28 is connected to the capacitor 12 and GND. Further, a capacitor 32 and a resonator 34 are connected in series to the output terminals TB and GND. The resonators 18 and 34 may be either dielectric resonators or stripline resonators.

Of these elements, the input side capacitor 16 and the resonator 18 constitute a first trap circuit 20. Capacitors 10, 12, 14, 24,
A bandpass filter (BPF) 30 is configured by 28 and the inductances 22 and 26. Further, the output side capacitor 32 and the resonator 34 form a second trap circuit 36. That is, the basic characteristics are obtained by the BPF 30, and the effect of removing unnecessary components by the trap circuits 20 and 36 is added to the characteristics to obtain the entire characteristics.

FIG. 2 shows the measured frequency characteristics of the prototype circuit of the first embodiment constructed as described above. The figure (A) shows the characteristics of the passing wave and the figure (B) shows the characteristics of the reflected wave. In the figure, the attenuation on the high frequency side is the action of the BPF 30.
The attenuation peaks PA and PB on the low frequency side are the trapping action of the two trap circuits 20 and 36.

Comparing this characteristic with FIG. 10 which is the characteristic of the background art, first, 1.658 shown by the peak P2.
The degree of attenuation at GHz is about 54 dB in the present embodiment, compared with about 37 dB in the background art,
The degree of attenuation on the low frequency side is steep. This P
The peak position indicated by 2 can be easily changed by replacing the corresponding one of the resonators 20 and 36. Further, the degree of attenuation at 1.907 GHz indicated by P3, which is the passband, is about 1.0 dB in the present embodiment, while the background art is about 1.2 dB, and the insertion loss is reduced. There is.

FIG. 3 shows the measured values of the frequency characteristics of the BPF according to this embodiment and the BPF according to the background art up to 6 GHz, and FIGS. 3A and 3B show the characteristics of this embodiment. , (C) and (D) show the characteristics of the background art. Further, (A) and (C) show the characteristics of the passing wave, and (B) and (D) show the characteristics of the reflected wave. In FIG. 7C, the third harmonic component of 5.721 Hz, that is, 3f, which is indicated by P4, has a large peak, but it is well reduced in this embodiment of FIG. This is because, in this embodiment, the dielectric resonator is not used as a bandpass filter but is used as a trap circuit.

It is considered that such good characteristics are due to the fact that the traps by the resonators 22 and 30 have a higher Q than the LC traps. As a result, the high attenuation described above,
A filter device having a low loss characteristic can be obtained. In other words,
When the same frequency characteristic as in the case of using the LC trap is obtained, the Q of the resonator can be lowered, and as a result, the resonator can be downsized, that is, the parts can be downsized and lightened.

<Second Embodiment> Next, a second embodiment will be described with reference to FIG. The second embodiment is an example of HPF. The circuit configuration is shown in FIG. 3A, and capacitors 50, 52, and 54 are connected in series between the input terminal TA and the output terminal TB. Between the input terminal TA and GND,
A trap circuit 60 including a capacitor 56 and a resonator 58 is connected. A coil 62 is connected between the output side of the capacitor 50 and GND, and a coil 66 is connected between the output side of the capacitor 52 and GND. The HPF 68 is configured by these. Further, a capacitor 70 is provided between the output terminals TB and GND.
And a trap circuit 74 constituted by the resonator 72 are connected.

FIGS. 2B and 2C show the frequency characteristics obtained by actual measurement of the prototype circuit. (B) is a passing wave,
(C) is the characteristic of the reflected wave. The attenuation on the low frequency side is mainly due to the action of HPF68. Also, the attenuation peak P
C and PD are trap functions by the trap circuits 60 and 74.

<Third Embodiment> Next, a third embodiment will be described with reference to FIG. The third embodiment is an example of LPF. The circuit configuration is shown in FIG. 3A, and coils 80, 82, 84 are connected in series between the input terminal TA and the output terminal TB. A trap circuit 90 including a capacitor 86 and a resonator 88 is connected between the input terminal TA and GND. A capacitor 92 is connected between the output side of the coil 80 and GND, and a capacitor 96 is connected between the output side of the coil 82 and GND. The LPF 98 is composed of these. A trap circuit 104 including a capacitor 100 and a resonator 102 is connected between the output terminals TB and GND.

FIGS. 2B and 2C show frequency characteristics obtained by actual measurement of a prototype circuit. (B) is a passing wave,
(C) is the characteristic of the reflected wave. The attenuation on the high frequency side is mainly due to the action of LPF98. Also, the attenuation peak P
E and PF are trap actions by the trap circuits 90 and 104.

<Fourth Embodiment> Next, a fourth embodiment will be described with reference to FIGS. These examples show specific examples of the BPF of the filter device according to the present invention. In the example shown in FIG. 6, the input side capacitor 11
The HPF 116 is composed of 0 and 112 and the coil 114, and the LPF 126 is composed of the output side capacitors 118 and 120 and the coils 122 and 124. Then, the capacitor 128 and the resonator 130 form a first trap circuit 132, and the capacitor 134 and the resonator 136 form the second trap circuit 1.
38 are configured.

In the example shown in FIG. 7, the LPF 144 is composed of the capacitor 140 and the coil 142, and the HPF for the primary frequency (fundamental wave) is composed of the capacitor 146. Capacitor 148 and resonator 1
The first trap circuit 152 is constituted by 50, and the LPF for the primary frequency is constituted by the coil 154. In addition, the coil 156 and the capacitor 15
HPF1 for secondary frequency (second harmonic) by 8
60 are configured. Capacitor 162 and resonator 16
2 comprises a second trap circuit 166, and a capacitor 168 forms an HP for the primary frequency.
F is configured.

In the example shown in FIG. 8, capacitors 170, 1
BPF 178 is composed of 72 and coils 174 and 176, and capacitors 180 and 182 and coil 18 are provided.
The HPF 188 is composed of the 4, 186. The capacitor 190 and the resonator 192 constitute a first trap circuit 194, and the capacitor 196
The second trap circuit 200 is constituted by the resonator 198. The coil 176 of the BPF 178 and the capacitor 172 constitute the trap circuit 202. In addition, the capacitor 180 of the HPF 188 and the coil 1
The trap circuit 204 is also configured by 84.

<Other Embodiments> The present invention can be variously modified based on the above disclosure, and includes, for example, the following. (1) In the above embodiment, as shown in FIG. 9 (A), the resonator 302 is connected in series to the capacitor 300, and the capacitor 3
00 and the equivalent inductance 304 of the resonator 302 are resonated in series to form a trap circuit. However, the figure (B)
Connect the resonator 302 to the coil 308, as shown in
The coil 308 and the equivalent capacitance 306 of the resonator may be resonated in series to form a trap circuit.

(2) Further, the number of stages of the filter circuit and the trap circuit is arbitrary, and the number of connection stages may be appropriately increased or decreased as necessary. (3) The configuration of the filter circuit is arbitrary and may be any circuit configuration. Further, an LC trap and a resonator trap according to the present invention may be provided. (4) The frequency band of the filter and the frequency of the trap may be appropriately set as necessary, and are not limited to the above graph of characteristics.

[0023]

As described above, according to the present invention, since the trap circuit is configured using the resonator, it is possible to obtain the ideal filter characteristics while reducing the size and weight of the parts. Further, there is an effect that the number of elements constituting the circuit can be reduced, and the cost and the loss can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a graph showing frequency characteristics of the first embodiment.

FIG. 3 is a graph showing the frequency characteristics of Example 1 in comparison with the background art.

FIG. 4 is a diagram showing a circuit configuration and frequency characteristics of a second embodiment.

FIG. 5 is a diagram showing a circuit configuration and frequency characteristics of a third embodiment.

FIG. 6 is a circuit diagram showing a first example of Example 4;

FIG. 7 is a circuit diagram showing a second example of the fourth embodiment.

FIG. 8 is a circuit diagram showing a third example of the fourth embodiment.

FIG. 9 is a circuit diagram showing still another embodiment.

FIG. 10 is a diagram showing a circuit configuration and frequency characteristics of the background art.

[Explanation of symbols]

10, 12, 14, 16, 24, 28, 32, 50, 5
2,54,56,70,86,92,96,100,1
10,112,118,120,128,134,14
2,146,148,158,162,168,17
0, 172, 180, 182, 190, 196 ... Capacitors 18, 34, 58, 72, 88, 102, 130, 13
6,150,164,192,198 ... Resonator 20, 36, 60, 7490, 104, 132, 13
8, 152, 166, 194, 200 ... Trap circuit 22, 26, 62, 66, 80, 82, 84, 122,
124, 140 ... Coil 30, 178 ... BPF 68, 116, 158, 188 ... HPF 98, 126, 140 ... LPF 304 ... Equivalent inductance 306 ... Equivalent capacitance 36, 94, 98 ... LPF 38, 40, 60, 74, 90 , 104 ... Trap circuit 64, 68 ... HPF PA, PB, PC, PD, PE, PF ... Attenuation peak TA ... Input terminal TB ... Output terminal

Claims (2)

[Claims] 1. A filter circuit including a capacitor and a coil; a structure in which a resonator and a capacitor are connected in series, and the equivalent inductance of the resonator and the series capacitor resonate in series in the attenuation region of the filter circuit. A high-frequency filter device equipped with a trap. 2. A filter circuit including a capacitor and a coil; a structure in which a resonator and a coil are connected in series, and an equivalent capacitance of the resonator and a series coil resonate in series in an attenuation region of the filter circuit. A high-frequency filter device equipped with a trap.