JPS60261201A - Microwave filter - Google Patents

Abstract

PURPOSE:To make the titled filter small in size, to reduce a loss, and also to suppress an unnecessary resonance mode by installing a dielectric resonator in the inside of a cut-off waveguide, and connecting a waveguide type resonator formed by a passing waveguide to input and output ends. CONSTITUTION:An incident microwave is filtered by using a resonance frequency of a waveguide type resonator as a center frequency, a microwave whose length between inductive metallic rods 5, 6 is half-wavelength resonates, and an unnecessary resonance mode scarcely exists. Subsequently, the microwave enters a cut-off waveguide 1 and it is further filtered by two dielectric resonators 2 whose tranmisstion loss is small. However, the resonator 2 has many resonance modes, therefore, the unnecessary resonance mode can be eliminated by providing the waveguide type resonator again on an output side of the last stage and making is pass through.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to microwave filters.

[Prior art]

Up until now, there has been a demand for improved performance of microwave filters in order to realize high-quality lines.Microwave filters using waveguide resonators have excellent signal selectivity, but they suffer from loss. big? Moreover, it has the disadvantage that the device becomes large-sized.

On the other hand, micro-wave filters and filters using dielectric resonators are being put into practical use because they can be made smaller in size, have less loss, and have good temperature characteristics. However, since a dielectric resonator is equipped with a dielectric material with a high dielectric constant, it inherently has many resonance modes, and when a fill is formed, its transmission characteristics and anti-resonance characteristics cause many unnecessary resonances. was occurring. FIG. 1 is a plan view of a conventional microwave filter using a dielectric resonator.

A dielectric resonator 2 is mounted inside the cutoff waveguide 1,
A pass waveguide 8 is connected to both ends of the cutoff waveguide l.

Note that 4 indicates a flange. In this type of filter, there are many resonance modes determined by the dimensions and dielectric constant of the dielectric resonator. This resonance mode is, for example, the Institute of Electronics and Communication Engineers Microwave Research Fund MW 78-56' 1978, 7
May, Kobayashi 2 Tanaka "Mode chart of open-end dielectric cylindrical resonator", IEEE, VOl, MTT-16, PP21
0-218 APr, 1968W, H, Harrjso
n, 'A Miniature High-QBa
nd pass FiltGr Employing
Dielecflc, :”','j5mResonat
ors, and an example is given below, and the dielectric constant εr=32.9. Diameter D = 7.3 (3 exposed, total length - 4, for a 2151 dielectric, the resonant frequency is 8 GHz as HEIII mode and 8.7 GHz as E210 mode.

9.2 GHz as H011 mode, HIIJI
IO, 4GHz as I mode, IO, 7GHz as EOII mode.

Resonance occurs at 11.4 GHz as EHIII mode.

FIG. 2 and FIG. 8 are diagrams showing the transmission characteristics and 0 reflection characteristics of conventional microwave filters using dielectric resonators, respectively, where fo in the figures represents the center frequency and a represents the unnecessary resonance mode. ing.

If a filter with such a large number of unnecessary resonance modes is used in a microwave transmitter, it may emit unnecessary waves and cause interference not only with the own system but also with other systems. In this case, unnecessary waves will be received and the line quality will deteriorate. Furthermore, when used as a channel demultiplexing filter, it has the disadvantage of adversely affecting other channels.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a microwave filter that is small, has low loss, and can suppress unnecessary resonance modes.

[Structure of the invention]

A microwave filter according to the present invention is formed by a dielectric resonator installed in a cutoff waveguide and a passing waveguide connected to an input end and/or an output end of the cutoff waveguide. It is characterized by being composed of a waveguide type resonator.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a plan view of a four-stage microwave filter according to an embodiment of the present invention, and FIG. 5 is a sectional view taken along the line X--X in FIG. 4. l to 4 are equivalent to those in Figure 1, and 5
, 6 is an inductive metal rod installed in the passing waveguide 8, and 7 is a center frequency adjustment screw. Unlike conventional dielectric filters, inductive metal rods 5 and 6 are installed inside the passing waveguide 8 at an interval of approximately half the wavelength within the passing waveguide 8 as resonators at the input and output parts. A dielectric resonator 2 is installed inside the cutoff waveguide l. That is, the resonators on the input side and the output side are of waveguide type, and the resonator at the center is made of a dielectric material to obtain predetermined microwave filter characteristics.

First, the incident microwave is filtered using the resonant frequency fO of the waveguide resonator on the input side as a center frequency. By the way, in a waveguide type resonator, microwaves whose length is half a wavelength between the inductive metal rods 5 and 6 resonate, and there are very few other unnecessary resonance modes. The microwave then enters the cutoff waveguide 1 and is further filtered by two dielectric resonators with very low transmission losses. However, since a dielectric resonator essentially has many resonance modes, the transmitted waves and reflected waves of this resonator include many unnecessary resonance modes. Therefore, by providing a waveguide resonator again on the output side, which is the final stage, and allowing the microwave to pass through, the above-mentioned unnecessary resonance mode can be removed.

In other words, by using waveguide resonators that contain almost no unnecessary resonance modes as resonators on the input and output sides, the unnecessary resonance modes inherent to the dielectric resonator in the center are suppressed, and the transmission characteristics are improved. It may not appear or it may be of a very low level. Furthermore, in terms of reflection characteristics, since most of the energy is reflected by the waveguide resonator on the input side or the output side, unnecessary resonance modes can be suppressed to an unobservable level. FIG. 6 shows the transmission characteristics, and FIG. 7 shows the reflection characteristics.

In the above embodiment, a case where a waveguide resonator is provided on both the input and output sides has been described, but a similar effect can be obtained in a structure in which a waveguide resonator is provided only on either the input side or the output side. Thus, an even smaller microwave filter can be realized.

〔Effect of the invention〕

As explained above, according to the present invention, a microwave filter that is very useful in practice has both the advantages of a dielectric filter that is small and has low transmission loss and the advantages of a waveguide filter that has very few unnecessary resonance modes. can be provided.

[Brief explanation of the drawing]

Figure 1 is a plan view of a conventional microwave filter using a dielectric resonator, Figures 2 and 3 are transmission characteristics, reflection characteristics, and transmission characteristics of the microwave filter shown in Figure 1, respectively. 4 is a plan view of a microwave filter according to an embodiment of the present invention, FIG. 5 is a sectional view taken along the line X-X in FIG. 4, and FIGS. 6 and 7 are respectively FIG. 4. FIG. 1 is a transmission characteristic diagram of the microwave filter shown in FIG. 1・・・・・・・・・Cut-off waveguide. 2・・・・・・Dielectric resonator. 3...... Passing waveguide. 4...Flange. 5.6... Inductive metal rod. ７・・・・・・・・・Center frequency adjustment screw. fo: Center frequency. Patent Applicant NEC Corporation Agent Uchihara Otoku′・′”.

Claims (1)

[Claims] It has a dielectric resonator installed in a cutoff waveguide, and a waveguide resonator formed by a passing waveguide connected to the input end and/or output end of the cutoff waveguide. A microwave filter characterized by: