JPS62157402A - Dielectric filter - Google Patents

Abstract

PURPOSE:To obtain a filter having a desired band width by selecting a characteristic impedance and a propagation constant of a transmission line so as to form easily two poles caused at an attenuation region to optional positions being asymmetrical to the center frequency. CONSTITUTION:Through holes 3... are formed at a proper interval in a dielectric block 1 made of a titanium group ceramic dielectric or the like. An inner conductor 4 made of a metallic film is formed in the inner face of the through holes 3..., short-circuited with an outer conductor 2 by a conductive film formed to the bottom face of the dielectric block 1, and dielectric resonators A1, A2... are constituted by each inner conductor 4, the outer conductor 2 and the dielectric block 1 existing among them. In skipping two resonators A2, A3, when the resonators A1, A4 are coupled by using a semi-rigid cable having capacitor electrodes 9, 9 at both ends, two poles P1, P2 are formed at both sides of the center frequency fo in the filter characteristic of the dielectric filter 1. The location of the two poles P1, P2 is easily changed to optional asymmetric positions with respect to the center frequency fo by selecting the characteristic impedance and the propagation constant of the semi-rigid cable 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dielectric filter having a configuration in which a plurality of dielectric resonators are coupled to each other electromagnetically or via a coupling element, and in particular relates to This paper relates to a proposal for a bandpass type dielectric filter with a pole at .

The applicant of the present application, Juren Eri, previously wrote in Japanese Patent Application No. 60-218753,
We proposed a bandpass type dielectric filter with a pole in the attenuation region. According to this proposal, if two dielectric resonators are skipped and the dielectric resonators in front and behind them are directly coupled with a reactance element, both the attenuation range higher than the center frequency and the attenuation range lower than the center frequency can be achieved. It is possible to form poles at approximately symmetrical positions with respect to the center frequency. The presence of this pole makes the rise of the filter characteristics steeper, which can meet the needs of users who require at least a certain amount of attenuation at a predetermined frequency away from the center frequency. It has the advantage of being easier.

By the way, the inventor of the present invention was conducting a test to confirm the technical value of the previously proposed technology.
We confirmed that by adding a certain configuration, it is possible to set the poles that occur on both sides of the center frequency at asymmetric positions with respect to the center frequency. The ability to set the two poles that occur in the attenuation range at asymmetric positions with respect to the center frequency increases the degree of freedom in filter design and is very useful.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a useful dielectric filter in which a pole is formed at a position asymmetric with respect to the center frequency as described above, and in which this asymmetry can be easily controlled.

In order to achieve the above object, the present invention uses a distributed constant type transmission line in which at least two dielectric resonators are skipped and the dielectric resonators existing before and after the dielectric resonators have a reactance element at both ends. They are characterized by being connected to each other.

Figure 5 shows an equivalent circuit of the dielectric filter of the present invention. In the figure, At, A2... are dielectric resonators, k is a coupling element (coupling element or three-dimensional circuit that performs electromagnetic coupling) that couples each dielectric resonator AI, A2..., and P is a distribution. The constant type transmission lines Xi and X2 are actance elements connected to both ends of the transmission line l. This figure shows a case where the series circuit of reactance elements XI, X2 and transmission line β is connected to resonators Al and A4 before and after the two dielectric resonators A2 and A3, bypassing the two dielectric resonators A2 and A3.

By the way, the transmission line l constitutes a distributed constant circuit, and if its characteristic impedance is zO1 and the propagation constant is θ, then Zo = 1E, bottom −−−−−−−−−−−−+1) θ
= F `` -・-・-・-(2) However, since the transmission line length is short, it is assumed that it is a lossless line.

When the equivalent circuit of FIG. 5 is rewritten using the above equation, it becomes as shown in FIG. 6. And x1, x2 in this circuit. L/
2. If we convert the T-type circuit consisting of C into a π-type circuit, the seventh
This results in the circuit shown in the figure. In this circuit, the value of X1' is dominated by C. Here, C is +1), (2
) is a function of 20 and θ, and θ is a linear function of frequency, so L and C change their values as the frequency changes. Therefore, Zo,
By selecting transmission lines with different angles of θ, low frequency performance can be achieved.

The value of C, the range in the high range, and the value of C can be varied. Therefore, if polarization of the filter characteristics is realized using a leaf constant circuit, the poles will be generated at positions symmetrical to the center frequency, but in the case of the present invention, the poles will be generated at positions asymmetrical to the center frequency. At the same time, the asymmetry can be controlled freely.

Figure 1 shows a dielectric filter constructed of dielectric resonant blocks as an embodiment of the present invention, 1 is a dielectric block made of a titanium oxide ceramic dielectric, etc., and the four sides of the block 1 are An outer conductor 2 made of a metal film is formed on the
Inside the dielectric block 1, through holes 3 are formed at appropriate intervals.
・is formed. An inner conductor 4 made of a metal film is formed on the inner surface of the through hole 3, and is short-circuited to the outer conductor 2 by a conductive film (not shown) formed on the bottom surface of the dielectric block 1 (hereinafter, this Shorten the bottom of the dielectric block #
It is called 8 end faces. ). A dielectric resonator A1 . . . is formed by each of the inner conductors 4 . A2... (hereinafter referred to as a resonator at the end) is configured. Resonator A1. Coupling holes 6, which serve as a means for coupling the resonators to each other, are formed between the resonators A2, . . . , and the adjacent resonances iA1, A2, . When the resonators are coupled through the coupling holes 6, the coupling is inductive. Dielectric filters having such a structure are known.

7 is a semi-rigid cable as an example of a transmission line,
The outer skin 7a is fixed by soldering to the earth case 8 connected to the outer conductor 2 of the dielectric block 1, and the one-way edge 7
b is a dielectric block 1 with no metal film formed on both ends.
It is connected to capacitor electrodes 9, 9 formed on the outer surface 1a (hereinafter referred to as the open end surface). Capacitor electrode 9°9 connects two resonators A2. It has a constant distance from the inner conductor 4 of the resonators At and A4, which exist before and after A3, and is electrostatically coupled to the resonators Al and A4 by the capacitance determined by the distance.

In this way, two resonators A2. If A3 is skipped and the resonators Al and A4 existing before and after A3 are connected to each other with a semi-rigid cable 7 having capacitor electrodes 9 and 9 at both ends, the filter characteristics of the dielectric filter 1 are as shown by the solid line in Fig. 2. There are two poles Pi on both sides of the center-to-center wave number fO as shown in
P2 is possible.

As described in the operation section, the poles Pi and P2 can be easily changed to any asymmetric position with respect to the center frequency "0" by selecting the characteristic impedance ZO1 and the propagation constant θ of the semi-rigid cable 7.

In the above configuration, the reactance elements XI and X2 are connected to the resonator A.
As shown in FIG. 3, a dielectric bushing 10 is inserted into the π through hole 3, and a metal pin 11 is inserted into the bushing 10.
and the inner conductor 4 on the inner wall of the tribute hole 3. Alternatively, although not shown, a leaded capacitor or a chip capacitor may be used as the reactance element. For leaded capacitors, the leads can be soldered directly to the open end of the inner conductor. In the case of a chip type capacitor, one capacitor electrode may be connected and fixed to a terminal attached to the open end of the inner conductor 4, and the extension line of a semi-rigid cable may be connected to the other capacitor electrode.

Furthermore, the reactance element is not limited to a capacitance g element, but may also be an inductance element 12 as shown in FIG. However, the use of the inductance element 12 is limited to the case where the coupling element k shown in the equivalent circuit of FIG. 2 is capacitive.

This is because unless this is the case, two poles cannot occur in the filter characteristics. Further, in the case of an inductance element, it is desirable to insert it into the through hole 3 from the short-circuit end face 1b side as shown in the figure. In the figure, 13 is an insulating bushing for holding the inductance element 12.

Although not shown, transmission lines include coaxial cables such as semi-rigid cables as shown in Figure 1.
It goes without saying that strip lines can also be used. Further, as long as two poles are formed, three or more resonators can be skipped and the resonators existing before and after the resonators can be connected by a transmission line having reactance elements at both ends.

Note that the dielectric resonators are not limited to those formed integrally in a single dielectric block as in the illustrated example;
It is also possible to use so-called dielectric coaxial resonators configured one by one independently. In that case, each resonator is coupled via a coupling element such as a capacitor.

As explained above, according to the present invention, by selecting the characteristic impedance and propagation constant of the transmission line, the two poles occurring in the attenuation region can be positioned at arbitrary positions asymmetrical with respect to the center frequency. It is easy to form, a filter with a desired bandwidth can be obtained more easily than ever before, and there is also the effect of increasing the degree of freedom in filter design.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a dielectric filter as an embodiment of the present invention, FIG. 2 is a diagram showing filter characteristics of the filter, and FIGS. 3 and 4 show actance elements that can be used in the present invention. 5 is a diagram showing an equivalent circuit of the dielectric filter of the present invention, FIG. 6 is a diagram showing a circuit in which the transmission line in FIG. 5 is equivalently converted by an LC element, and FIG. FIG. 3 is a diagram showing a circuit in which a part of the circuit is equivalently converted to a π type. Ai A2. A3. A4. A5...Dielectric resonator 7.
...Transmission line, XI, X2... Reactance element patent applicant Murata Manufacturing Co., Ltd. O-1-f Figure 3 Figure 4

Claims (1)

[Claims] In a dielectric filter in which a plurality of dielectric resonators are electromagnetically coupled to each other or coupled via a coupling element, at least two dielectric resonators are skipped before and after the dielectric filter. 1. A dielectric filter characterized in that dielectric resonators are coupled to each other using a distributed constant transmission line having reactance elements at both ends.