JPH05102707A - Dielectric filter - Google Patents

Abstract

PURPOSE:To obtain the dielectric filter having an attenuation pole at both sides of a pass band with simple configuration by providing at least one series connection comprising a dielectric coaxial resonator being a resonance element and an LC series circuit to the filter. CONSTITUTION:A BPF is formed by capacitance-coupling between a resonance circuit S2 of series connection comprising a dielectric coaxial resonator theta3 and an LC series circuit S1 and plural dielectric resonators theta1, theta2. Each circuit constant of the resonators theta1, theta2, the resonator theta3 being a component of the circuit S2, and an inductor L1 and a capacitor C3 is selected so that an anti- resonance point f0 of the circuit S2 is a center frequency of the pass band of the dielectric filter 1. Thus, the pass characteristic of the filter 1 is a characteristic having an attenuation pole at resonance points f1, F2 at both sides of the pass band DELTAW. As a result, the attenuation characteristic of the dielectric filter 1 is improved by the simple circuit configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit configuration of a dielectric filter constructed by using a dielectric coaxial resonator.

[0002]

2. Description of the Related Art As is well known, in a bandpass filter, attenuation characteristics at both ends of the band have been improved by providing attenuation poles on both sides of the pass band. In the coupled dielectric filter, the attenuation pole is provided on the low band side or the high band side of the pass band by the circuit configuration shown in FIG. 9 or 11.

FIG. 9 shows two dielectric coaxial resonators θ1 and θ.
2 and a series circuit S1 including a dielectric coaxial resonator θ3 and a capacitor C5 are coupled by coupling capacitors C1 and C2. Note that Ci is the input capacitance at the input terminal Pi, Co
Is the output capacitance at the output end Po.

This dielectric filter is based on the series circuit S1.
It has an attenuation pole at the frequency f4 corresponding to the resonance point in, and the attenuation pole appears on the low frequency side of the pass band as shown in FIG. 10, for example.

In FIG. 11, the two dielectric coaxial resonators θ1 and θ2 are coupled by a coupling capacitance C1, the dielectric coaxial resonator θ3 is coupled by an inductance L4, and further, the output end Po and the dielectric The coupling point A of the body coaxial resonator θ2 is coupled by a capacitor C7. In this dielectric filter, for example, an attenuation pole appears on the high frequency side of the pass band as shown in FIG.

[0006]

In the above conventional circuit configuration, the attenuation pole can be formed only on either the low band side or the high band side of the pass band, and the attenuation characteristics on both sides of the pass band are improved. It is difficult.

It is also conceivable to improve the attenuation characteristics on both sides of the pass band by combining the above-mentioned conventional circuit configurations, but this makes the circuit configuration complicated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a dielectric filter having attenuation characteristics on both sides of the pass band and having excellent attenuation characteristics.

[0009]

In order to solve the above-mentioned problems, the present invention adds a LC series circuit to one of the dielectric coaxial resonators to form poles on both sides of the pass band and to provide attenuation characteristics. To improve. An LC parallel resonance circuit may be used instead of the dielectric coaxial resonator.

[0010]

According to the present invention, the impedance characteristic of the series circuit of the dielectric coaxial resonator and the LC series circuit has an antiresonance point and resonance points on both sides of the antiresonance point.
Therefore, when the anti-resonance point is set to the center frequency of the pass band, the resonance point appears as an attenuation pole on both sides of the pass band of the filter, and the attenuation characteristic on both sides of the pass band is improved.

Further, in place of the dielectric coaxial resonator, an LC
Even when a parallel resonator is used, the impedance characteristic is similar to the above, and attenuation poles appear on both sides of the pass band.

[0012]

FIG. 1 is a diagram showing an embodiment of the circuit configuration of a dielectric filter according to the present invention. The dielectric filter 1 shown in the figure has two series of dielectric coaxial resonators θ1 and θ2, a series circuit S2 of the dielectric coaxial resonator θ3 and an LC series circuit S1.
Is a three-stage bandpass filter in which and are connected in cascade via coupling capacitors C1 and C2. Also, Ci is the input terminal P
Input capacitance for inputting a signal from i, and Co is an output capacitance for outputting a signal from the output end Po.

The dielectric coaxial resonators .theta.1 to .theta.3 each have a terminal short circuit 1 in which an outer peripheral surface, an inner peripheral surface and one end surface of a cylindrical dielectric made of, for example, ceramics are covered with a conductor.
It is composed of a quarter wavelength coaxial resonator. Further, the coil L1 and the capacitor C3 that form the LC series circuit S1.
Is composed of, for example, an air-core coil and a chip capacitor.

Impedance characteristic Z of the series circuit S2
Reference numeral 1 is a sum of the impedance Z2 of the dielectric coaxial resonator θ3 (shown by a chain line in the figure) and the impedance Z3 of the series circuit S1 (shown by a chain line in the figure). Resonance points (resonance frequencies) f1 and f2 (f) on both sides of the antiresonance point (antiresonance frequency) fo of the resonator θ3.
2>fo> f1), and the series circuit S2 alone has a transmission characteristic showing a pass characteristic at the anti-resonance point fo and an attenuation characteristic at the resonance points f1 and f2 as shown in FIG. ..

Regarding the circuit constants of the dielectric coaxial resonators θ1 and θ2 and the dielectric resonator θ3 constituting the series circuit S2, the inductance L1, the capacitance C3, etc., the anti-resonance point fo of the series circuit S2 is a dielectric filter. It is appropriately set to be the center frequency of the pass band of 1, so that the pass characteristic of the dielectric filter 1 has the attenuation poles at the resonance points f1 and f2 on both sides of the pass band ΔW as shown in FIG. It is a characteristic.

As described above, the dielectric coaxial resonator θ3 and LC
Since the resonance circuit S2 in which the series circuit S1 is connected in series and the plurality of dielectric coaxial resonators θ1 and θ2 are capacitively coupled to form a bandpass filter, the anti-resonance point fo of the resonance circuit S2 is desired. The resonance points f1 and f2 of the resonant circuit S2 appear as attenuation poles on both sides of the pass band ΔW by setting the center frequency of the pass band ΔW of the dielectric filter 1 with a simple circuit configuration. Can be planned.

In the above embodiment, the series circuit S2 of the dielectric coaxial resonator θ3 and the LC series circuit S1 is provided at the final stage of the dielectric filter 1, but it may be provided at the first stage or in the middle stage. May be.

FIG. 5 is a diagram showing a circuit configuration of a second embodiment of the dielectric filter according to the present invention. In this figure, a capacitor C4 is connected in series to the dielectric coaxial resonator θ1 shown in FIG. 1 to increase the attenuation pole on the low frequency side of the pass band ΔW. In this dielectric filter 1 ', as shown in FIG. 6, the resonance point f3 of the series circuit S3 of the dielectric coaxial resonator θ1 and the capacitor C4 occurs on the low frequency side of the pass band ΔW, and the resonance point f3 lowers the resonance frequency f3. An attenuation pole is newly formed on the region side.

Therefore, two attenuation poles f1 and f3 appear on the low frequency side of the pass band ΔW, and the attenuation characteristic is further improved. The attenuation pole f3 may be located on the higher frequency side than the attenuation pole f1.

FIGS. 7 and 8 show an embodiment of a circuit configuration for increasing the attenuation pole on the high frequency side of the pass band ΔW. FIG. 7 shows a configuration in which the coil L2 is provided in parallel with the series circuit S3 in FIG. In addition, in FIG. 8, a coupling coil L3 is provided in place of the coupling capacitance C1 in FIG. 6, and the coupling point B and the input end Pi of the dielectric coaxial resonator θ2 are provided.
The capacitors C6 are connected to each other.

According to these circuit configurations, the pass band ΔW
It is possible to newly increase the attenuation pole before and after the attenuation pole f2 on the high frequency side, and the attenuation characteristic on the high frequency side is further improved.

Since the resonance characteristic of the 1/4 wavelength dielectric coaxial resonator can be equivalently replaced with the resonance characteristic of the LC parallel resonant circuit, the LC coaxial resonator is replaced with the LC parallel resonator. May be used, and in this case, the same effect as described above can be obtained.

Further, in the above embodiment, the dielectric filter provided with one series circuit S2 in which the dielectric coaxial resonator and the LC series circuit are connected in series has been described.
Two or more may be provided.

[0024]

As described above, according to the present invention, at least one resonator in which a dielectric coaxial resonator and an LC series circuit are connected in series is provided as a resonance element, and the series circuit attenuates both sides of the pass band. Since the poles are formed,
A filter having a good attenuation characteristic can be configured with a simple circuit configuration.

In place of the above dielectric coaxial resonator, LC
The same effect as described above can be obtained by using a resonance circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a circuit configuration of a dielectric filter according to the present invention.

FIG. 2 is a diagram showing impedance characteristics of a series circuit of a dielectric coaxial resonator and an LC series circuit.

FIG. 3 is a diagram showing transmission characteristics of a series circuit of a dielectric coaxial resonator and an LC series circuit.

FIG. 4 is a diagram showing a waveform of a pass characteristic of the dielectric filter according to the present invention.

FIG. 5 is a diagram showing a circuit configuration of a second embodiment of the dielectric filter according to the present invention.

FIG. 6 is a diagram showing a waveform of a pass characteristic of a second embodiment of the dielectric filter according to the present invention.

FIG. 7 is a diagram showing a circuit configuration of an embodiment of a dielectric filter in which the attenuation pole on the low frequency side of the pass band is increased.

FIG. 8 is a diagram showing a circuit configuration of another embodiment of the dielectric filter in which the attenuation pole on the low frequency side of the pass band is increased.

FIG. 9 is a diagram showing an example of a circuit configuration of a conventional dielectric filter having an attenuation pole on the low frequency side.

FIG. 10 is a diagram showing a waveform of a pass characteristic of a conventional dielectric filter having an attenuation pole on the low frequency side.

FIG. 11 is a diagram showing an example of a circuit configuration of a conventional dielectric filter having an attenuation pole on the high frequency side.

FIG. 12 is a diagram showing a waveform of a pass characteristic of a conventional dielectric filter having an attenuation pole on the high frequency side.

[Explanation of symbols]

 Ci, Co, C1 to C8 capacitors L1 to L3 coils θ1 to θ3 dielectric coaxial resonator S1 LC series circuit S2, S3 series circuit Pi input end Po output end

Claims (2)

[Claims] 1. A dielectric coaxial resonator and an LC as a resonance element.
A dielectric filter comprising at least one serially connected series circuit. 2. The dielectric filter according to claim 1, further comprising an LC parallel resonance circuit in place of the dielectric resonator.