Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1982-09-27
1984-10-16
Nussbaum, Marvin L.
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333206, 333224, 333235, H01P 1205, H01P 704
Patent
active
044777868
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Technical Field
This invention relates to a band pass filter in which semi-coaxial cavity resonators are connected in multiple stages.
Background Art
A band pass filter in which semi-coaxial cavity resonators are connected in multiple stages is heretofore widely used to obtain sufficient selective characteristic and low loss property as a filter to be used in the VHF or UHF band. However, such a conventional filter requires very complicated adjustments to obtain desired band pass filter characteristic due to the fact that the resonance frequency and the characteristic impedance of the semi-coaxial cavity resonators in each stage affect adversely each other when connected in cascade. Further, it is necessary to maintain high dimensional accuracy of the respective portions of the filter, causing expensive production cost.
The inventors of the present invention have previously proposed, as disclosed in Japanese patent application No. 53-72569 (Japanese patent Laid-Open No. 54-163656), an inexpensive and readily adjustable band pass filter in which a rectangular cylinder made by cutting across a rectangular waveguide available in the market is used as an outer conductor (outer housing) of each stage, both opening ends of the cylinder are blocked with flat plates and an inner conductor is disposed in the outer conductor. Thus, the semi-coaxial cavity resonators of the respective stages are individually manufactured, are then adjusted in a predetermined resonance frequency, and are coupled integrally, thereby reducing the material cost and the number of adjusting steps.
The present invention principally follows the above-mentioned construction type, and this construction will be described in more detail in the later description of the embodiments of the present invention.
There has been a need for smaller mobile radio communication equipment such as automotive radio telephones and portable radio equipment, in which smaller components such as smaller filters must be employed. In order to meet this need, a filter such as disclosed in the Japanese patent application No. 52-15204 (Japanese patent Laid-Open No. 53-999849) has been proposed, in which a multiple of resonators are so constructed that a dielectric material 2 is filled in the space inside an outer conductor 1 of a semi-coaxial cavity resonator so as to surround an inner conductor 3 and is maintained in electric contact with the outer conductor 1 through an electrode 4 as shown in FIGS. 1 and 2 and the degree of coupling between the resonators is adjusted by a coupling adjustment screw 5. The resonators are connected in multiple stages. According to this conventional filter, the space between the inner conductors 3 and 3 can be reduced as compared with the case of an air-filled filter of the same band width, and the resonance frequency can be stabilized by compensating the influence of the thermal expansion of the outer and inner conductors 1 and 3 through properly chosing the temperature coefficient of the dielectric material 2.
However, a filter having such construction has obviously the following drawbacks and disadvantages.
When titanium oxide series ceramics having a good temperature characteristic is used as a dielectric material, the filter of the above-mentioned construction becomes very expensive in view of unit cost and amount used, and also becomes heavy.
Further, although the Japanese patent application does not disclose the frequency adjustment method of the respective resonators forming the filter, this adjustment cannot be considered easy. The adjustment of the filtering characteristic with a coupling adjustment screw 5 requires considerable skill.
Disclosure of Invention
This invention contemplates to eliminate the above-mentioned drawbacks and disadvantages of the conventional band pass filter and provides a band pass filter in which a semi-coaxial cavity resonator comprises a cylindrical conductor having a suitable section used as an outer conductor, an adequate dielectric substrate disposed in an air gap between an
REFERENCES:
patent: 3273083 (1966-09-01), Rose
patent: 4268809 (1981-05-01), Makimoto et al.
Daisuke Koga
Tamura Masahide
Nussbaum Marvin L.
Toyo Communication Equipment Co., Ltd.
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