JPS59114902A - Dielectric filter - Google Patents

Abstract

PURPOSE:To attain easily formation of a wide band by connecting the intra-hole conductors to each other which form a resonator by means of a capacitor. CONSTITUTION:A chip capacitor 5 is provided between resonators 2 respectively on a non-metallized outer surface (hole opening surface) 1a of a dielectric block 1. Then resonators (intra-hole conductors) 2 are connected to each other by those capacitors 5. Therefore the resonators 2 are connected to each other by the capacitor 5 in addition to the magnetic field connection using a gap formed between resonators 2. Thus it is possible to set optionally the coupling capacity between resonators 2 by selecting properly the capacity of the capacitor 5. In such a way, a wide band can be obtained easily.

Description

DETAILED DESCRIPTION OF THE INVENTION 0) Technical Field of the Invention The present invention relates to a dielectric filter, and more particularly to an improved structure of a band-pass filter (hereinafter abbreviated as rBPFJ) for widening the band.

(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 of such dielectric filters is provided with holes penetrating the dielectric block from one side to the opposite side, and the other required outer surfaces of the dielectric block except for at least one hole opening surface and the above-mentioned outer surface. There is a coaxial dielectric filter that has a conductive film formed on the inner surface of the hole.

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, and shows a dielectric block 1 (hereinafter simply referred to as "block").
A plurality of holes 2 are provided in the block 1 that penetrate from the - side to the opposite side, and the other five outer surfaces of the block 1 except one hole opening surface 1a (the upper surface in the figure) and the inner surface of the holes 2 are provided. A conductor film (indicated by tucking in the figure) is formed (metalized) using a method such as a thick film. In this case, the conductor film on the outer surface of the dike block 1 becomes the outer conductor, and the conductor film on the inner surface of the hole 2 becomes the inner conductor, so that the inner conductor of each hole 2 reduces the depth of the hole by 1/ A 1/4 wavelength resonator that resonates at frequencies of four wavelengths is constructed. Therefore, when both ends of the block 1 are connected to an external circuit via a suitable excitation body 3 (in the illustrated example, a C couple made of a conductive film pattern), the block 1 operates as a BPF. Note that 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.

Bα=Klj-fo・51 stones Here, Bα: Equal amplitude bandwidth fo: In-band center frequency giygj: Circuit element constant Kij: Coupling coefficient between resonators, usually the bandwidth Bα is determined by the coupling coefficient Kij. Ru. The coupling coefficient Kli is determined by the shape of the filter, etc., and it has been shown through actual research that it changes depending on the presence or absence of coupling adjustment holes and the distance between resonances, as shown in FIG. In addition, when the diameter of the coupling adjustment hole is increased, the coupling coefficient Kij
has the property of becoming larger.

That is, when designing a conventional BPF, the coupling coefficient Kij
was appropriately selected depending on the distance between the resonators and the diameter of the coupling adjustment hole. However, in this case, the fractional band (Bα/f0
) In order to increase the coupling coefficient Kij, it is necessary to shorten the distance between the resonators and enlarge the coupling adjustment hole, so that the resonators or the resonators and the coupling adjustment hole become closer together. This makes machining difficult. Particularly when the filter is miniaturized, processing becomes even more difficult.

In the end, with conventional filter structures, 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 problems of the conventional dielectric filter as described above, that is, to provide an improved structure that can easily achieve a wide band.

(5) Structure of the Invention The present invention provides a coaxial dielectric filter as described above, in which the inner conductors of the holes constituting the resonator are coupled to each other via a capacitor on the non-metallized large opening surface of the dielectric block. The structure is as follows.

(6) Embodiments of the invention Hereinafter, embodiments of the invention will be described in detail with reference to the drawings.

FIG. 3 shows a first embodiment of a coaxial dielectric filter according to the present invention.This filter has five resonators (holes) 2 formed therein, and coupling adjustment holes, compared to the conventional filter shown in FIG. The basic imitation is the same except that there is no 4.

Then, in place of the coupling adjustment hole 4, a chip capacitor 5 is provided between each resonator 2 on the unmetallized outer surface (hole opening surface) la of the block 1, and the resonators (Ouchi conductor) 2 are connected to each other. These are to be coupled through 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 (Ouchi conductor) is formed by metallization on the large opening surface 1a of the block 1.
c-conductor no. 4 turn 6 connects electrode 5 of capacitor 5 &
connected to.

According to the above configuration, in addition to the electromagnetic field coupling due to the gap between the resonators, the resonator 2 is also coupled by the capacitor 5. Therefore, by appropriately selecting the capacitance of the capacitor 5, the resonator 2 The coupling capacitance between the two can be set arbitrarily. As a result, when trying to widen the filter band,
By increasing the capacitance of the capacitor 5, it is possible to increase the coupling capacitance between the resonators, and since it is not necessary to bring the resonators close to each other, high accuracy is not required in processing. Incidentally, the capacitance of the capacitor 5 can be arbitrarily changed by appropriately selecting the capacitance of the dielectric chip itself and the gap d of the electrode 5a, which has the advantage of having a high degree of freedom in selecting the capacitance and also ensuring a large capacitance. .

FIG. 5 shows a second embodiment of a filter according to the invention. The basic structure of this filter is the same as the first embodiment shown in FIG. However, in this embodiment, a capacitor composed of four conductor turns 7 is used instead of a chip capacitor. The conductor AI ethanon is formed by metallization on the hole opening surface la of the block 1, and one end of each is connected to the resonator 2.
and the other ends thereof face each other with a gap d in between.

Therefore, by changing the capacitance of the capacitor by changing the gap d of the conductor pattern 7, the coupling capacitance between the resonators 2 can be changed. Finally, as in the case of the first embodiment, it is possible to increase the coupling capacitance between the resonators by increasing the capacitance of the capacitor 7, and since there is no need to bring the resonators closer together, the machining process becomes more expensive. Accuracy is not required. This second embodiment has the advantage that the capacitor 7 is easier to form and is less expensive than the first embodiment.

The above embodiments are all 1/4 wavelength resonant filters in which only one hole opening surface 1a of the block 1 is not metallized, but the other hole opening surface (bottom surface in the figure)
In the case of a 1/2 wavelength resonant filter which is not metallized, a capacitor 5 or capacitor 7 similar to that described above may be provided also on this hole opening surface.

(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 and without requiring high processing precision. Yes, the effect is significant.

[Brief explanation of the drawing]

Figure 1 is a schematic perspective view of a conventional example of a coaxial dielectric filter.
Fig. 2 is a graph showing the coupling capacitance characteristics of a coaxial dielectric filter, Fig. 3 is a schematic perspective view of the first embodiment of the dielectric filter according to the present invention, and Fig. 4 is a graph of the chip capacitor of the first embodiment. The enlarged perspective view, FIG. 5, is a schematic perspective view of a second embodiment of the present invention. 1... Dielectric block, IIL... Hole opening surface, 2.
... Hole (resonator), 3... Exciter, 5... Chip capacitor, 5a... Electrode, 6... Conductor A turn, 7
...Conductor 14' turn (capacitor). Patent applicant Fujitsu Limited Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Yukio Uchida Akira Yamaguchi Figure 1 Distance between resonators Figure 3

Claims (1)

[Claims] 1. A dielectric block is provided with a plurality of holes penetrating from one surface to the opposite surface, and at least one of the outer surfaces of the dielectric block except for the opening surface of the holes is provided, as well as other required outer surfaces and the inner surface of the holes. In a dielectric filter having a conductive film formed thereon, four of the holes constituting the resonator are coupled to each other via a capacitor at the large opening surface of the dielectric block on which the conductive film is not formed. A dielectric filter characterized by: