JPH0417481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a band pass filter (BPF) used in a wireless device, etc., and particularly relates to a multistage coaxial dielectric filter having a plurality of resonators.

(2) Background of the technology Conventionally, in general, for example, in-vehicle radio, mobile radio, etc.
BPF for VHF band and UHF band mobile radio equipment
A multi-stage coaxial filter is used as a multi-stage coaxial filter. There are many types of multistage coaxial filters, including cavity types. In recent years, dielectric filters, which have features such as small size, light weight, good temperature characteristics, and low loss, have come into widespread use.

However, conventional coaxial filters have problems as described below, and countermeasures are desired.

(3) Prior Art and Problems Figure 1 shows a conventional four-stage coaxial dielectric filter (hereinafter simply referred to as "filter"). This filter has four through holes 2 in a dielectric block 1 (hereinafter simply referred to as "block"), and the other five holes on the outer surface of the block 1 except for one hole opening surface 1a (top surface in the figure). A conductive film (indicated by hatching in the figure) is formed (metallized) on the surface and the inner surface of the hole 2. As a result, the conductive film on the outer surface of the block becomes the outer conductor, and the conductive film on the inner surface of the hole becomes the inner conductor, and the inner conductor of each hole 2 creates a resonator that resonates at a frequency whose depth is 1/4 wavelength. Configure. Therefore, both ends of block 1 are connected to suitable exciter 3.
(In the illustrated example, a C-couple made of a metalized conductor pattern) is connected to an external circuit.
The filter operates as a BPF.

However, in resonator 2, in addition to the fundamental frequency of ₀ , where the hole depth is 1/4 wavelength, the hole depth is 3/4, 5/4,
..., n/4 (n is an odd number) wavelength, and even odd-order harmonic components 3 ₀ , 5 ₀ , ..., n ₀ have the property of resonating. Therefore, the liquid passing through the filter becomes as shown in FIG. A filter like this on the transmitter
When used as a BPF, there is a problem in that harmonic components such as 3 ₀ , 5 ₀ , . . . amplified by the power amplifier of the transmitter also pass through the BPF and are sent out from the antenna. In particular, ₃₀ has a lot of energy and is very harmful.

(4) Purpose of the Invention The purpose of the present invention is to solve the problems of the conventional multi-stage coaxial filter as described above, that is, to effectively attenuate the harmonic components of the fundamental frequency, especially the high energy ₃₀ , and to reduce the Upper center frequency ₀
It is an object of the present invention to provide a dielectric filter with good high-order spurious characteristics that allows only the above-mentioned spurious signals to pass through.

(5) Structure of the Invention The multi-stage coaxial dielectric filter according to the present invention divides a resonator into a plurality of blocks, interposes a shielding layer of a conductor between adjacent blocks, and provides a high-frequency harmonic filter for the fundamental frequency in the shielding layer. A structural feature is that a coupling hole for coupling the resonators to each other is formed at the position of the minimum point of the electric field distribution of the wave component.

(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 filter according to the invention. This filter is basically the same as the dielectric filter shown in FIG. However, the block 1 is divided into two parts 1A and 1B, and a shielding plate 4 made of a conductive material is interposed between them. As shown in FIG. 4, a coupling window 5 is formed in the shielding plate 4. As shown in FIG. As shown in Fig. 5, the position of the coupling window 5 is the position of the point _P0 where the electric field distribution of the harmonic component ₃₀ is minimum, that is, approximately 2/3 H from the bottom when the height of the block 1 is H. It is located at
Therefore, between the resonators 2A and 2B (FIG. 3), the center frequency ₀ can pass through the coupling window 5, but the center frequency ₃₀
can only pass through the coupling window 5 and is greatly attenuated. As a result, the spurious characteristic of ₃₀ is the 6th
It is improved as shown in the figure. In this case, the spurious characteristics of ₅₀ are not improved, but the energy thereof is quite small, so it is unlikely to be a problem in practice.

FIG. 7 shows a second embodiment of the invention. In this example, the block 1 is divided into three parts 1A, 1B, and 1C, and a shielding plate 4 as shown in FIG.
A and 4B are interposed, and the spurious characteristics of ₃₀ are further improved compared to the case shown in FIG. Also,
In this embodiment, if the central block portion 1B is further divided into two parts and a shielding plate is interposed between them, ₃₀ will be attenuated for each coupling stage of the resonator 2, resulting in an extremely good result. Spurious characteristics can be realized. Furthermore, in this embodiment, each shielding plate 4
If the coupling windows 5 of A, 4B, ... are formed at different positions such as the minimum point of electric field distribution at ₃₀ and the minimum point of electric field distribution at ₅₀ , high-order spurious not only at ₃₀ but also at ₅₀ or higher will be generated. Properties are also improved.

FIG. 8 shows a third embodiment of the invention. This embodiment has a structure in which a conductive film is formed on the side surface 1b of the block portion 1B except for the coupling window 6, without using a shielding plate as described above. In this case as well, effects similar to those of the embodiment shown in FIG. 3 can be obtained.

In the case of the first and second embodiments shown in FIGS. 3 and 7, the shielding plates 4, 4A, 4B, . It is also possible.

(7) Effects of the Invention As described above, according to the present invention, it is possible to realize a multistage coaxial filter with excellent high-order spurious characteristics that can effectively attenuate harmonic components other than the fundamental frequency to be passed.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of an example of a conventional coaxial dielectric filter, FIG. 2 is a graph showing the characteristics of the filter shown in FIG. 1, and FIG. 3 is a first embodiment of a coaxial dielectric filter according to the present invention. 4 is a side view of the shielding plate, FIG. 5 is an explanatory diagram of the electric field distribution of the dielectric filter, FIG. 6 is a graph showing the characteristics of the first embodiment, and FIG. 7 is a diagram showing the characteristics of the first embodiment. A schematic perspective view of the second embodiment,
FIG. 8 is a schematic perspective view of a third embodiment of the present invention. 1...Dielectric block, 1A, 1B, 1C...
Block part, 1a... Hole opening surface, 2, 2A, 2
B...hole (resonator), 3...exciter, 4,4A,
4B... Shielding plate, 5, 6... Combined window.

Claims (1)

[Claims] 1. In a multi-stage coaxial dielectric filter having multiple resonators, the resonator is divided into multiple blocks, a shielding layer of a conductor is interposed between adjacent blocks, and harmonic components of the fundamental frequency are interposed in the shielding layer. A filter characterized in that a coupling hole for coupling resonators to each other is formed at the position of the minimum point of the electric field distribution.