JPS6277703A - Dielectric filter - Google Patents

Abstract

PURPOSE:To obtain a desired band pass characteristic without increasing number of resonators by connecting plural dielectric resonators connected side by a side with a reactance element at an interval of >=1 resonator. CONSTITUTION:Resonators A2 and A5 at an interval of >=1 resonator among the resonators A1-A6 coupled electromagnetically through a coupling hole 6 and constituting the dielectric filter are connected to a reactance element having lands 7c via gaps G1, G2. Thus, a pole is given to the attenuation region of the filter and a band-pass filter having a desired frequency characteristic is obtained without increasing number of stages of the resonator.

Description

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

From the user side, in a follow-up bandpass filter,
We sometimes receive orders for filters under the condition that the amount of attenuation at frequencies a predetermined frequency away from the center frequency is greater than or equal to a predetermined value. In this case, in order to satisfy the above requirements in a filter in which a plurality of adjacent resonators are electromagnetically coupled or coupled via a coupling element, regardless of whether they are cavity resonators or dielectric resonators, the resonator One method is to increase the number of resonator stages, but one way to meet the above requirements without increasing the number of resonator stages is to skip one or more resonators and directly electromagnetically couple the resonators before and after it. There is a way. According to this method, poles Pi and P2 occur in the attenuation region, as shown by solid lines in FIG. 16, and the filter characteristics become sharp. Therefore, as a result, the amount of attenuation at a frequency that is a predetermined frequency away from the center frequency exceeds a predetermined value, thereby satisfying the above requirement. In the figure, the broken line indicates the frequency characteristics of a filter with the same number of resonator stages and no poles.

By the way, the technique of creating a pole in the attenuation range of the filter characteristics as described above (hereinafter referred to as polarization) is already known and has been implemented in cavity resonator filters and semi-coaxial filters, but it is not applicable to dielectric filters. The current situation is that it has not been implemented yet.

However, with the recent spread of dielectric resonators, there is a demand for dielectric filters using them to be polarized.
Its development is urgently needed.

The present invention was proposed based on such a request, and includes a dielectric filter having a configuration in which a plurality of dielectric resonators are electromagnetically coupled to each other or coupled via a coupling element. It is characterized by skipping one dielectric resonator and directly connecting the dielectric resonators before and after it with a reactance element.

Figure 1 shows a dielectric filter constituted by a dielectric resonance block as an embodiment of the present invention, and 1 is a dielectric block made of a titanium oxide ceramic dielectric or the like; An outer conductor 2 made of a metal film is formed on the four sides,
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 conductor B* (not shown) formed on the bottom surface of the dielectric block 1 (hereinafter referred to as The bottom surface of this dielectric pro-7 is called the short-circuit end surface.) Dielectric resonators At, A2, etc. (hereinafter simply referred to as resonators) are constituted by the inner conductors 4, the outer conductors 2, and the dielectric block 1 present therebetween. Resonator A1. A coupling hole 6 as a means for coupling the resonators to each other is provided between A2...
... are formed, and adjacent resonators AI, A2, ... are electromagnetically coupled. When the resonators are coupled through the coupling holes 6, the coupling is inductive. Dielectric filters having such a structure are known.

The upper surface 1a of the dielectric block 1 is an open end surface on which no conductive film is formed, and two resonators A3. A4
, and the resonators A2. A glue actance element is formed to connect A5. In the illustrated example, the reactance element is realized by a conductive pattern 7 formed of silver paste or the like on the open end surface. That is, the conductive pattern 7 has a land portion 7a connected to the inner conductor 4 of the resonator A2, a land portion 7b connected to the inner conductor 4 of the resonator A5, and a gap Gl between the land portions 7a and 7b. , and a land portion 7C whose ends face each other via G2, and the gaps G1 and G2 constitute a capacitive element, which is an example of a reactance element.

As mentioned above, two resonators A3. A4 is skipped and the resonator A2. If A5 is connected with a capacitance element, the filter characteristics will have poles Pi and P2 in the upper and lower attenuation regions, as shown in FIG. The positions of the poles Pi and P2 vary depending on the magnitude of the impedance of the actance element. Generally, the higher the impedance, the more the pole tends to move away from the center frequency fO. Note that in the case of low impedance, the pole enters the passband, which is not preferable.

The poles are determined by the number of resonators that are skipped by connecting reactance elements, the type of reactance element (capacitive or inductive), and the type of element that couples each resonator (coupling hole or coupling element such as reactance). It can be selectively formed in one of the upper and lower attenuation regions depending on whether it is capacitive or conductive. Now, as shown in the equivalent circuit of the dielectric filter in FIG. 2, if the reactance element is X and the coupling element is k, the positions of the generated poles are as shown in the table below. However, in the table, C means capacitive and L means inductive.

The capacitive element as an example of the front reactance element
In addition to being formed by a conductive pattern as shown in the figure, it can also be formed by the configurations shown in FIGS. 3 to 7. In the example shown in FIG. 3, resonator A2. Capacitor electrode patterns 8a and 8b are formed at predetermined intervals from the inner conductor 4 of A5, and these electrode patterns 3a and 8b are connected to the resonator A2. A5 inner conductor 4
A capacitance is formed between the two. In this case, the two capacitor electrode patterns 8a and 8b can be connected by a lead wire 8C, or can be formed integrally with the conductive pattern 7C as in the above example. The device shown in FIG. 4 uses a capacitor element 9 with leads to ensure the above-mentioned capacitance.

Leads 9a and 9b of this element 9 connect to the resonator A2. It is installed at a position closer to the open end surface of the inner conductor 4 of A5. If a trimmer capacitor element is used as the capacitor element 9, the capacitance thereof can be changed and the pole generated in the attenuation region can be moved, which is convenient for adjustment. The one shown in Figure 5 is the resonator A2.
．． Insert the insulator 10 into the through hole 3 of A5, and
Both ends of a conductor rod 11 such as a lead wire are inserted into the inner conductor 4 to form a capacitance between the conductor rod 11 and the inner conductor 4. In this case, the insertion point of the tip of the conductor rod 11 may be the coupling hole 6. In the case of the coupling hole 6, the tip of the conductor rod 11 can be directly attached to the wall surface of the coupling hole. Note that in these examples, the capacitor element 9 can also be used instead of the conductor rod 11. Figure 6 shows the short-circuited end face 1 of the conductor rod 11.
An example is shown in which it is inserted into the coupling hole 6 from the b side. In this way, even if the short-circuited end is inserted into the coupling hole 6, the conductor rod 11 can be capacitively coupled to the resonator, thus forming a capacitor in the same manner as on each side described above. . What is shown in FIG. 7 is a modification of FIGS. 3 and 4, in which the inner conductor 4 and capacitor electrode pattern 9a of resonators A2 and A5 are shown.

8b, and both patterns 8b.
A and 8b are connected by a trimmer capacitor 12.

Next, FIG. 8 shows an example in which a coil L is used as the beam actance element X. That is, a conductive pattern 138.13b having one end connected to the inner conductor 4 of the resonators A2 and A4 is formed on an open end surface, and a coil element is connected to the other ends of both patterns. According to this configuration, since the number of skipped resonators is 1 and k and X are inductive, it is possible to obtain a bandpass filter having a pole only in the upper attenuation region, as is clear from the above table.

Coil element and resonator A2. The connection structure with A4 is the 9th
As shown in the figure, the lead wire p1 of the coil element. i2 directly into the resonator A2. It may be connected to the A4 inner conductor 4, or the coil element itself may be inserted into the coupling hole 6 from the short-circuit end surface 1b side as shown in FIG. 10. In this case, it is preferable to fill the coupling hole 6 with an insulator 14 to hold the coil element so that the coil element does not wobble. One end of the coil element is connected to the shorting electrode 15 on the shorting end face 1b.

FIG. 11 shows an example in which the reactance element X is composed of a composite circuit of a capacitor and a coil.

The capacitor component consists of two conductive patterns 16 and 17 formed on the open end surface and the resonator A2. The coil component consists of two conductive patterns 16 and 17.
It is composed of a coil element connected between the two. Although the table above does not list the case in which the actance element X is constructed from a composite circuit of a capacitor and a coil, polarization can be achieved.

FIGS. 12 to 14 each show specific configurations for easily realizing the filter of the present invention. It goes without saying that the filter of the present invention can be realized in the previous embodiments, but the filter of the present invention essentially requires a high impedance element as the reactance element X. In the case where a capacitance element is used as a reactance element, the value of the capacitance element must be 0.05 pF or less, so this can be realized, for example, by connecting a plurality of capacitors in series. However, it is extremely difficult to stably manufacture such a low capacity, and even if the capacity changes slightly during installation, the ratio of the variation to the original capacity is large, resulting in a pole occurring in the attenuation range. There is a problem that it moves a lot and it is difficult to obtain a filter with desired characteristics. Therefore, we have solved these problems and made it possible to stably obtain a filter with desired characteristics with good reproducibility by using a capacitor with a large capacity that is easy to manufacture.
This is an embodiment shown in FIG.

The embodiment shown in FIG. 12 has a resonator A2. A capacitor conductor m pattern 2 is placed on the open end surface at a predetermined distance from the inner conductor 4 of A5.
Both putters formed 1.22.

The cables 21 and 22 are connected by an extension line 23a of a semi-rigid cable, and the outer sheath 23b of the semi-rigid cable is connected to a ground case 24.

According to this configuration, the resonators A2. A capacitance is formed between the inner conductor 4 of A5 and the capacitor electrode patterns 21 and 22, and a capacitance is also formed between the inner wire 23a and the earth case 24 via the outer cover 23b. Therefore, if expressed as an equivalent circuit, it is as shown in FIG. 15(a). In the figure, C
1, C2 is the capacitance between the inner conductor of the resonator and the capacitor electrode pattern, and C3 is the capacitance between the inner wire of the semi-rigid cable and the outer sheath, and thus the ground. Here, since the above C1, C2, and C3 are star (Y) connected,
If this is equivalently converted into a delta (Δ) connection as shown in the same figure (b), the impedance of the reactance element X is determined as follows.

・ jωC3 Now, if Zl=22=23, the above equation becomes Z1=Z2=2
3=□. Therefore, in that case, capacitor CI,
By using C2 and C3 with a capacitance three times that required for the reactance element X, a large capacitance of 0.15 pF can be used for 2.03, which makes manufacturing very easy.

The embodiments shown in FIGS. 13 and 14 are basically the same as the embodiment shown in FIG.
It consists of a circuit in which C2 and C3 are Y-connected. However, in the embodiment shown in FIG. 12, the capacitance C3 is constituted by a fixed capacitance between the extension wire 23a and the outer sheath 23b of the semi-rigid cable, but in the embodiment shown in FIG. 13, two capacitor electrode patterns 21. The embodiment shown in FIG. 14 consists of a capacitor element or a trimmer capacitor element 26 provided between a lead wire 25 connecting the lead wire 22 and the ground case 24, and the embodiment shown in FIG. screw 26
They differ in their composition. In the figure, 27 is a metal cover. The capacitance C3 can be configured with a trimmer capacitor element, or the capacitance C3 can be configured with a metal screw 2 as in the embodiment shown in FIG.
6, the value of the reactance element X is also changed equivalently, so that the pole generated in the attenuation region can be moved, which is convenient for adjustment.

In the embodiments shown in FIGS. 12 to 14, the capacitances C1 and C2 are connected to the resonators A2. Although it is constructed between the inner conductor of A5 and the capacitor electrode patterns 21 and 22, it can also be constructed between two opposing conductive patterns as shown in Fig. 1, or as shown in Fig. 5. As described above, the tip of the lead wire (or cable extension wire) can be inserted into the through hole 3 or the coupling hole 6 of the resonator, and the structure can be formed between the tip and the inner conductor 4. Further, all of the illustrated embodiments show examples in which the present invention is applied to a dielectric filter composed of a dielectric resonator block in which a plurality of dielectric resonators are integrally formed. It goes without saying that the present invention can be applied to a dielectric filter having a configuration in which resonator elements each having a single resonator element are connected via a coupling element such as a capacitor.

As described above, according to the present invention, it is possible to provide a dielectric filter using a dielectric resonator with a pole in the attenuation range, thereby creating a band having frequency characteristics that meet the user's requirements. There is an effect that a pass filter can be obtained without increasing the number of stages of dielectric resonators.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing a dielectric filter as an embodiment of the present invention, Fig. 2 is an equivalent circuit diagram of a dielectric filter as an embodiment of the invention, and Figs. FIG. 15(a) is an equivalent circuit diagram of the filter shown in FIG. 12, and FIG. 15(b) is a partial or partial diagram showing another embodiment of the invention. FIG. 16 is a diagram showing the frequency characteristics of the bandpass filter. AI, A2. A3. A4. 'A5...Dielectric resonator X
... Reactance element patent applicant Murata Manufacturing Co., Ltd. Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 13 Figure 14

Claims (1)

[Claims] (1) In a dielectric filter having a configuration in which a plurality of dielectric resonators are electromagnetically coupled to each other or coupled via a coupling element, at least one dielectric resonator is skipped, and the dielectric material existing before and after the dielectric resonator is skipped. A dielectric filter characterized by a resonator directly connected to a reactance element.