JPH04135301A - Dielectric filter - Google Patents

Abstract

PURPOSE:To obtain an enough attenuation in the state of suppressing a loss in a passing band at a minimum by providing an attenuation band pass filter using a distributed constant type resonator which impedance is smaller than that of a dielectric coaxial type resonator. CONSTITUTION:A band pass filter 2 composed of more than one dielectric coaxial type resonators, and an attenuation band pass filter 1 using the distributed constant type resonator, whose resonance frequency is in the passing band of band pass filter 2 and whose impedance is smaller than that of the dielectric coaxial type resonator, are provided. Namely, the impedance of the resonator used for an attenuation band is set so as to become smaller than the impedance of the dielectric coaxial type resonator used for a pass band. Thus, in combination with the filter 2, the enough attenuation can be obtained in the state of suppressing the loss in the pass band to a minimum.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a dielectric filter in which the characteristic impedance of an attenuation band filter combined with the pass band filter is adjusted in order to improve the attenuation characteristics of the pass band filter. be.

[Prior Art] This type of dielectric filter combines a passband filter made of a plurality of dielectric coaxial resonators with an attenuation bandpass filter. That is, a passband filter generally used in an antenna duplexer or the like is combined with an attenuation bandpass filter to attenuate the high frequency side, the low frequency side, or both of the passband (see Fig. 1). In FIG. 1, the characteristic curve indicated by the symbol (a) is the attenuation characteristic of the pass band filter, and the change in the characteristic curve when the attenuation band filter is combined with this characteristic curve is indicated by the symbol (b).

[Problem to be solved by the invention] However, when the attenuation band is attenuated beyond a certain attenuation amount,
As shown by the symbol (c) in FIG. 1, it is necessary to make the amount of attenuation of the attenuation pole larger than necessary.

In other words, as shown in Figure 2, when trying to lower the level down to -50 dB, the loss within the passband must be large in order to obtain an attenuation that results in the characteristic curve indicated by the dashed-dotted line, which is lower than the characteristic curve indicated by the dotted line. (It will become.

In other words, a dielectric band coaxial resonator is generally constructed by filling a dielectric between an inner conductor and an outer conductor, but the characteristics required here are a large relative permittivity (εr) and low loss (Q is high). However, the Q of the dielectric resonator is determined by the following equation.

Q=(2/δ,)・(β・βn(b/a)/(21
n(b/a)+A (1/a+1/b))) Furthermore,
Here, a: outer diameter of inner conductor, b: inner diameter of outer conductor, δ8
; skin depth; β; resonator length. As is clear from the above equation, the value of Q is largely related to the ratio of a and b. Theoretically, Q is maximum at b/a=3.6, and increases in proportion to the diameter. Therefore, a dielectric coaxial resonator used in a passband filter is designed to have a b/a cape of 3.6 to minimize losses within its passband.

On the other hand, the characteristic impedance Z. is also related to a, b, and ε of the dielectric coaxial resonator, and is given by the following equation.

Z 0= (138/JE r) 4og(b/a)
Therefore, if a resonator is designed so that b/a = 3.6 in order to increase Q, the value will be 2° 76.7/7, r, and the characteristic impedance Z0 will be proportional to 1/7ε1. . However, if a high Q is desired, generally ε
, = about 20 to 100, Zo is 7 to n(t-A). However, if you try to use the same dielectric coaxial resonator that was used for the passband filter as is for the attenuation band filter, as mentioned earlier,
A resonator with ε = 20 to 100 and Z = 7 to 12 (ohms) has a small amount of attenuation (ATT) in the attenuation band, so that the initial objective cannot be achieved.

[Object of the Invention] The present invention has been made based on the above circumstances, and by appropriately setting the characteristic impedance of the attenuation band filter,
It has been discovered that a sufficient amount of attenuation can be obtained while minimizing the loss within the passband, and an attempt is made to provide a dielectric filter that focuses on this point.

[Means for Solving the Problems] Therefore, the present invention provides a passband filter configured using one or more dielectric coaxial resonators, and a resonant frequency that is in the passband of the passband filter and whose impedance is is equipped with an attenuation band filter using a distributed constant resonator smaller than that of the dielectric coaxial resonator.

In this case, the distributed constant type resonator is preferably a dielectric coaxial type resonator. Further, the attenuation bandpass filter preferably has a configuration in which a capacitance or inductance is connected in series to a dielectric coaxial resonator.

Furthermore, the attenuation band filter may be magnetically coupled to the resonator of the pass band filter. Further, the dielectric coaxial resonator used in the attenuation band filter is desirably set so that the ratio of the inner diameter of its outer conductor to the outer diameter of its inner conductor is smaller than 3.6.

[Example] Hereinafter, examples studied in realizing the dielectric filter of the present invention will be specifically explained with reference to the accompanying drawings. Here, we will move away from the conventional idea of setting b/a = 3.6 to obtain a high Q, and instead introduce an attenuation bandpass filter using several distributed constant resonators, especially a dielectric coaxial resonator. Let us examine the experimental results regarding the characteristics of .

FIG. 3 shows a circuit configuration in which the pass band filter 2 and the attenuation band filter 1 are combined. Here, "Zo" in the attenuation band filter 1 represents capacitance or inductance, and the pass characteristics of the attenuation band filter 10 are as shown in FIG. It will look like Figure 4 (b). That is,
When a capacitor is connected in series with a dielectric coaxial resonator, the curve becomes steeper on the higher frequency side than the attenuation pole, and becomes gentler on the lower frequency side. If the inductances are connected in series, the opposite will occur. Therefore, in terms of implementation, an attenuation band filter in which a capacitor is connected in series with a dielectric coaxial resonator is used when it is desired to attenuate frequencies lower than the pass band of the pass band filter, An attenuation band filter with an inductance connected to is used when you want to attenuate frequencies higher than the passband.

The experimental example shown below is for the former case. Here, by changing the value of b/a, the characteristic inbuildance Zo can be changed to 6.8, 10.12 (, t-A
), the capacitance is adjusted so that the frequency of the attenuation pole is the same for all attenuation band filters. As a result, the obtained transmission characteristics are as shown in FIGS. 5 and 6.

Such an attenuation band filter is called a pass band filter (b/
If we look at the attenuation amount of the filter device combined with a = 3, 6), for example, in the case of an attenuation band filter with z0 = 6 (Tom), it will be as shown in Figure 7 (b), and the two will be compared. Then, as shown in FIG. 8, it can be seen that an increase in attenuation of about 4.4 dB is brought about within the attenuation band with almost no loss in the pass band. Here, if ε, = 40, the resonator for the attenuation bandpass filter at Z0 = 12 (t-A) is b/a = 3.6, but 20 = [i
At (t-m) it is b/a 2.8. In this way, the effect of increasing the amount of attenuation becomes more obvious as x=3.6-b/a becomes larger.

In this way, if the impedance of the resonator used in the attenuation band is smaller than the impedance of the dielectric coaxial resonator used in the passband, sufficient attenuation can be obtained while minimizing loss within the passband. .

The attenuation band filter may be magnetically coupled to the resonator of the pass band filter. Furthermore, a combline dielectric resonator may be used as the passband filter and the attenuation band filter. The resonator may include the pass band filter and the attenuation band filter in the same block. Furthermore, the attenuation band filter may be interdigitally coupled to the pass band filter.

[Effects of the Invention] As described in detail above, the present invention is set so that the impedance of the resonator used in the attenuation band is smaller than the impedance of the dielectric coaxial resonator used in the pass band, so that it can be used as a pass band filter. In this combination, a sufficient amount of attenuation can be obtained while minimizing the loss within the passband.

[Brief explanation of the drawing]

Figure 1 is a graph showing a characteristic curve when a passband filter is combined with an attenuation band filter, and Figure 2 is a graph of a characteristic curve showing the state of loss within the passband as the amount of attenuation increases in the conventional method. , Figure 3 is a circuit diagram of the dielectric filter of the present invention, Figures 4 (a) and (b) are graphs of characteristic curves corresponding to the connection of capacitance and inductance to the resonator, and Figures 5 and 6 are graphs of characteristic curves corresponding to the connection of capacitance and inductance to the resonator. Graphs of characteristic curves shown by experimental values in the attenuation band and passband, Figures 7(a) and (b)
) is a graph showing a characteristic curve when the above-mentioned attenuation band filter is combined with a pass band filter, and FIG. 8 is a comparison graph clearly showing the effects of the present invention. ■...Attenuation band filter 2...Pass band filter agent Patent attorney Jo Taira'@, Deaf ll1II&11 ~-Ta-machi i

Claims (6)

[Claims] (1) A passband filter configured using one or more dielectric coaxial resonators, the resonance frequency of which is in the passband of the passband filter, and whose impedance is higher than that of the dielectric coaxial resonator. A dielectric filter comprising an attenuation band filter using a small distributed constant resonator. (2) The dielectric filter according to claim 1, wherein the distributed constant type resonator is a dielectric coaxial type resonator. (3) The dielectric filter according to claim 2, wherein the attenuation band filter has a configuration in which a capacitor is connected in series to a dielectric coaxial resonator. (4) The dielectric filter according to claim 2, wherein the attenuation band filter has a configuration in which an inductance is connected in series to a dielectric coaxial resonator. (5) The dielectric filter according to claim 1, wherein the attenuation band filter is magnetically coupled to a resonator of the pass band filter. (6) The dielectric material according to claim 2, wherein the dielectric coaxial resonator used in the attenuation band filter is set such that the ratio of the inner diameter of the outer conductor to the outer diameter of the inner conductor is smaller than 3.6. filter.