JPH0369202B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a dielectric filter, and particularly to an improved structure for widening the band of a bandpass filter (hereinafter abbreviated as "BPF").

(2) Background of the technology In recent years, dielectric filters have been used as BPFs for in-vehicle radios and portable radio devices called mobile radios, which have features such as smaller size, lighter weight, lower temperature coefficient, and lower loss than conventional helical filters. is used.

One such dielectric filter has a hole penetrating the dielectric block from one side to the opposite side,
There is a coaxial dielectric filter in which a conductive film is formed on the outer surface of a dielectric block other than at least one hole opening surface and on the inner surface of the hole constituting a resonator.

However, as will be described later, conventional coaxial dielectric filters have a problem in that, due to their structure, it is not easy to widen the band, and this becomes even more difficult as the filter becomes smaller.

(3) Prior art and problems Figure 1 shows a schematic configuration of a conventional example of a coaxial dielectric filter. A hole 2 is provided in one of the outer surfaces of block 1.
A conductor film (indicated by hatching in the figure) is formed (metallized) by a method such as a thick film on the other five outer surfaces of the hole opening surface 1a (upper surface in the figure) and on the inner surface of the hole 2. As a result, the conductor film on the outer surface of block 1 becomes an outer conductor, and the conductor film on the inner surface of hole 2 becomes an inner conductor, so that the inner conductor of each hole 2 makes the depth of the hole 1/4 wavelength. A 1/4 wavelength resonator that resonates at this frequency is constructed. Therefore, when both ends of the block 1 are connected to an external circuit via a suitable exciter 3 (in the illustrated example, a C couple formed by a conductive film pattern), the block 1 operates as a BPF. still,
The non-metalized holes 4 formed between the resonators 2 are holes for adjusting the amount of coupling between the resonators 2.

It is well known that the passband width of the above filter is determined by the following equation.

B〓＝K _ij・f _p・√ _i・_jWhere , B〓: Equal amplitude bandwidth f _p : In-band center frequency g _i , g _j : Circuit element constant K _ij : Coupling coefficient between resonators In other words, Usually the bandwidth B〓 is determined by the coupling coefficient K _ij . The coupling coefficient K _ij is determined by the filter shape, etc., and experiments have revealed that it changes depending on the presence or absence of coupling adjustment holes and the distance between resonances, as shown in FIG. Furthermore, when the diameter of the coupling adjustment hole is increased, the coupling coefficient K _ij increases.

That is, when designing a conventional BPF, the coupling coefficient K _ij was appropriately selected depending on the distance between the resonators and the diameter of the coupling adjustment hole. But in this case,
Coupling coefficient to increase fractional bandwidth (B〓/f _p )
If you try to increase K _ij , it is necessary to reduce the distance between the resonators or make the coupling adjustment holes larger, which causes the resonators or the resonators and the coupling adjustment holes to become closer, making processing difficult. Become. Particularly when the filter is miniaturized, processing becomes even more difficult.

In the end, with the conventional filter structure, extremely high-precision machining is required to increase the amount of coupling without changing the cross-sectional area of the resonator.

(4) Purpose of the Invention The purpose of the present invention is to solve the above-mentioned problems in conventional dielectric filters, that is, to provide an improved structure that can easily expand the band.

(5) Structure of the invention A plurality of through holes are provided in parallel in a rectangular parallelepiped dielectric block, and a conductor film is provided on the inner surface of the plurality of holes that constitute a resonator and on four surfaces parallel to the axis of the hole. In the formed dielectric filter, the present invention provides a conductor film pattern connecting to the inner conductor films of the plurality of holes constituting the resonator, on the hole opening surface of the dielectric block, in parallel with the axis of the holes. It is characterized in that it is provided so as not to come into contact with the conductor film formed on the surface, and the conductor film patterns are capacitively coupled by arranging them facing each other at a predetermined interval.

(6) Embodiments of the Invention Prior to describing embodiments of the present invention, a coaxial dielectric filter that couples resonators using a capacitor will be described as a reference example with reference to FIG. Compared to the conventional filter shown in Fig. 1, this filter has a
The basic structure is the same except that two resonators (holes) 2 are formed and there is no coupling adjustment hole 4.

Then, instead of coupling adjustment hole 4, block 1
Non-metallized outer surface (hole opening surface) 1
A chip capacitor 5 is provided between each resonator 2 on a, and the resonators (hole conductors) 2 are coupled to each other via these chip capacitors.
As shown in FIG. 4, the chip capacitor 5 has electrodes 5a formed on both sides of a dielectric chip by metallization. The resonator 2 (hole conductor) is connected to the electrode 5a of the capacitor 5 by a conductor pattern 6 formed on the hole opening surface 1a of the block 1 by metallization.

According to the above configuration, the resonator 2 has a capacitor 5
Therefore, by appropriately selecting the capacitance of the capacitor 5, the coupling capacitance between the resonators 2 can be arbitrarily set. As a result, when trying to widen the band of the filter, it is possible to increase the capacitive coupling between the resonators by increasing the capacitance of the capacitor 5, and there is no need to bring the resonators closer together, so high precision processing is not required. . In addition, capacitor 5
It is said that the capacitance can be changed arbitrarily by appropriately selecting the capacitance of the dielectric chip itself and the gap d of the electrode 5a (Fig. 4), and that the degree of freedom in selecting the capacitance is high and that a large capacitance can be secured. There are advantages.

FIG. 5 shows an embodiment of a dielectric filter according to the present invention. This filter has a plurality of through holes 2 arranged in parallel in a dielectric block 1 having a rectangular parallelepiped shape, and includes an inner surface of the plurality of holes 2 that constitute a resonator, four surfaces parallel to the axis of the hole, and the holes 2. One of the two hole opening surfaces perpendicular to the axis of dielectric block 1 (i.e., dielectric block 1
The basic structure is the same as that of the reference example shown in FIG. 3. However, in this embodiment, a capacitor composed of conductive patterns 7 is used instead of a chip capacitor.
The conductor patterns 7 are formed by metallization on the hole opening surface 1a of the block 1, one end of each is connected to the resonator 2, and the other ends are opposed to each other with a gap d in between. Therefore, the gap d of the conductor pattern 7
The coupling capacitance between the resonators 2 can be changed by changing the dimensions of the conductor patterns of the opposing portions and changing the capacitance. In other words, the third
Similar to the case where the capacitance of the capacitor 5 is increased in the reference example shown in the figure, it is possible to increase the coupling capacitance between the resonators, and there is no need to bring the resonators closer together, so high accuracy is not required in the processing. The embodiment of the present invention has the advantage that it is easier to form a capacitance using the conductive pattern 7 and the cost is lower than when the capacitor 5 is used as in the case of FIG. 3.

In all of the above embodiments, only one hole opening surface 1a of the block 1 is not metalized.
In the case of a 4-wavelength resonant filter, the other hole opening surface (bottom surface in the figure) is also not metalized.
In the case of a two-wavelength resonant filter, a capacitive coupling portion may also be formed on this hole opening surface using the same conductor pattern 7 as described above. Further, the hole 4 shown in the conventional example of FIG. 1, which is not formed with a conductive film, may be formed separately from the hole 2 forming the resonator, and the amount of coupling between the resonators 2 may be adjusted. .

(7) Effects of the Invention As described above, according to the present invention, in the coaxial dielectric filter as described above, it is possible to widen the band by simple structural improvement without requiring high processing accuracy. The effect is significant.

[Brief explanation of drawings]

Figure 1 is a schematic perspective view of a conventional example of a coaxial dielectric filter, Figure 2 is a graph showing the coupling capacitance characteristics of a coaxial dielectric filter, and Figure 3 is a coaxial dielectric that couples between resonators using a capacitor. FIG. 4 is an enlarged perspective view of the chip capacitor shown in FIG. 3, and FIG. 5 is a schematic perspective view of a dielectric filter according to an embodiment of the present invention. 1... Dielectric block, 1a... Hole opening surface, 2
... Hole (resonator), 3 ... Exciter, 5 ... Chip capacitor, 5a ... Electrode, 6 ... Conductor pattern, 7 ... Conductor pattern.

Claims (1)

[Claims] 1. A dielectric filter in which a plurality of through holes are provided in parallel in a rectangular parallelepiped dielectric block, and a conductive film is formed on the inner surfaces of the plurality of holes that constitute a resonator and on four surfaces parallel to the axis of the holes. In this method, a conductive film pattern connected to the inner conductive films of the plurality of holes constituting the resonator does not come into contact with the conductive films formed on four sides parallel to the axis of the holes on the hole opening surface of the dielectric block. 1. A dielectric filter characterized in that the conductor film patterns are capacitively coupled by arranging them facing each other at a predetermined interval.