JPS59117302A - Filter - Google Patents

Abstract

PURPOSE:To attenuate the 3rd harmonic component by selecting the position of a coupling hole of coaxial dielectric resonators to a position where an electric field by the 3rd harmonic component of the fundamental frequency is minimized. CONSTITUTION:Dielectric blocks 1A, 1B are provided respectively with two through-holes 2, 2A, and 2B, 2C and all faces except the upper face of each dielectric block and counter faces of each dielectric block are metallized to constitute a coaxial 1/4 wavelength resonator. Moreover, in the electric field distribution of the resonator, since a coaxial inner conductor is short-circuited at the bottom of the dielectric block and opened at the upper face, the electric field component of the 3rd harmonic of the fundamental frequency is minimized at a position corresponding to 2/3 of the said inner conductor, while the electric field in the fundamental frequency is slightly less than the maximum value. Thus, the filter reducing effectively the 3rd harmonic is constituted by inserting a shielding plate 4 having a coupling hole at the said position to a counter part of the said coaxial dielectric resonators.

Description

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

(2) Background of the Technology Conventionally, multi-stage coaxial filters are generally used as BPFs in VHF band and UHF band mobile radio devices such as in-vehicle radios and portable radios. 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 "
(abbreviated 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 completely formed (metalized) 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 constitutes a resonator that resonates at a frequency whose Z wavelength is the depth of the hole. . Therefore, if 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 metalized transparent pattern), the filter operates as a BPF.

However, the resonator 2 has a fundamental frequency f whose wavelength is the depth of the hole. In addition, the depth of the hole is %, 5/4-1-(
is an odd number) harmonic component of an odd order with wavelength fO+
” fO, ..., rLfo also have the property of resonating.Therefore, the passing wave of the filter is null as shown in Figure 2.When such a filter is used as a BPF of a transmitter, the power amplifier of the transmitter 3fo amplified by
There is a problem in that harmonic components such as sfo, . . . also pass through the BPF and are sent out from the antenna. In particular, 3
fo has a large amount of energy and is extremely harmful.

(4) Purpose of the Invention The purpose of the present invention is to solve the problems in the conventional multistage coaxial filter as described above, namely, to effectively attenuate the harmonic components of the fundamental frequency, especially 3fo-'i, which have large energy; substantially the center frequency f. The object of the present invention is 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 multistage coaxial electric shield filter according to the present invention is generally configured such that the resonators are coupled to each other at the minimum point of the electric field distribution of harmonic components of the fundamental frequency. It is something.

(6) Embodiments of the Invention Embodiments of the present 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, block 1 can be divided into two parts I
It is divided into A and IB, 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. The position of the coupling window 5 is a point P where the electric field distribution of the harmonic component 3fo is minimum, as shown in FIG. , that is, when the height of the block 1 is H, the position is approximately V3·H from the bottom surface.

Therefore, between the resonators 2A and 2B (FIG. 3), the center frequency f. can pass through the coupling window 5, but 3fO can only pass through the coupling window 5 to a small extent and is greatly attenuated. As a result, the spurious characteristics of 3FO are improved as shown in FIG. In this case, the spurious characteristics of 5f0 are not improved, but since the energy thereof is quite small, 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 LA, IB, and IC, and a shielding plate 4A as shown in FIG. 4 is provided between each part.

4Bi is interposed, and the spurious characteristics of 3fo are further improved compared to the case of FIG. In addition, in this embodiment, if the central block portion IB is further divided into two and a shielding plate is interposed between them, 3f0 will be attenuated for each coupling stage of the resonator 2, which will be extremely effective. It is possible to realize spurious characteristics. Furthermore, in this embodiment, if the coupling windows 5 of each shielding plate 4A, 4B, . High-order spurious characteristics of 5f0 or higher can also be 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 IB except for the coupling window 60 portion, 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 plate 4. It is also possible to form the blocks 4A, 4B, . . . not as independent parts, but integrally with the metal casing that houses the block 1.

(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 the drawing]

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. FIG. 8 is a schematic perspective view of the second embodiment of the invention, and FIG. 8 is a schematic perspective view of the third embodiment of the present invention. 1... Dielectric block, ], A, IB, IC... Block part, 1a... Hole opening surface, 2, 2A, 2B... Hole (resonator), 3... Exciter, 4.4A, 4B... Shielding plate, 5.6... Combined window. Patent Applicant Fujitsu Limited Patent Application Agent Patent Attorney Akira Aomi Patent Attorney Kazuyuki Nishidate Patent Attorney 1) Shino Patent Attorney Akiyuki Yamaguchi Figure 1 Figure 2 f, Jio 10 Frequency Figure 3 Figure 4 Figure 6 @ Figure 7 Figure 8

Claims (1)

[Claims] 1. A multistage coaxial dielectric filter having a plurality of resonators, characterized in that the resonators are coupled to each other at the minimum point of the electric field distribution of harmonic components of the fundamental frequency.