Bandpass type filter having tri-plate line resonators

Details Bandpass type filter having tri-plate line resonators Bandpass type filter having tri-plate line resonators

1993-01-08

1994-05-10

Ham, Seungsook

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

333205, 333238, H01P 1203

Patent

active

053111591

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

Field of the Invention
The present invention relates to a bandpass type filter, particularly to a bandpass type filter using resonators constituted by tri-plate lines.
Background of the Invention
A conventional bandpass type filter using a dielectric substrate is constituted by sequentially coupling a plurality of resonators and has predetermined bandpass characteristics around resonance frequencies thereof. In these resonators, many resonance modes (excitation modes) appear dependent on the shape and dimensions of the element. Basic resonance modes used in general are a TE.sub.018 mode TE.sub.018 resonator), a TM.sub.010 mode (TM.sub.010 resonator), and a TEM mode (TEM resonator). If the resonance frequency is the same in these modes, the sizes of the resonance systems become smaller in the order through the TE.sub.018 mode, the TM.sub.010 mode, and the TEM mode, whereas the values of unload Q also become smaller in the same order. For a filter used in a mobile communication device, since loco weight and a small size are required characteristics, the TEM mode resonator is utilized. Particularly, a coaxial TEM resonator of 1/4.lambda. mode is frequently used.
FIGS. 9 (a) to 9 (c) are views showing structure of conventional bandpass type filters using TEM resonators. FIG. 9 (a) shows a filter using coaxial line type dielectric resonators. In the filter, coaxial line type resonators (TEM resonators 102) are separately constructed and are sequentially coupled in a metallic case 101. Furthermore, input/output terminals and coupling circuit (not shown) are constructed in a metallic lid 103. FIG. 9 (b) shows a structure for a general TEM resonator filter. This TEM resonator filter is a type recently most widely used, and in which input/output terminals (input/output coupling electrodes 105), TEM resonators 106, and coupling circuits 107 are integrally constructed in one dielectric block 104. In order to separate each of the resonators, slits 108 for electric separation of adjacent resonators are inserted between the resonators. Reference number 109 denotes a ground conductor electrode.
FIG. 9 (c) shows structure of a microstrip line type filter. This filter is constituted by a ground conductor 110, a dielectric 111, input/output terminals 112, TEM resonators 113, and coupling circuits 114.
One application of such a filter may be an antenna duplexer. The antenna duplexer is an antenna sharing device in which a receiving filter with respect to the receiving frequency of a weak signal inputted from a common antenna, and a transmitting filter with respect to the transmitting frequency of a power signal outputted to the antenna are coupled with one terminal which is connected to the shared antenna. This antenna duplexer is one of important components of a bidirectional communication system which may be represented by a mobile telephone system. The antenna duplexer can be apparently seen as a combination of two filters, and matching of the shared terminal of the filters has been already done during the design stage of the filters, so that a manufacturer of the duplexer need not execute the matching.
With miniaturization of communication devices, the manufacturers of such devices have been strongly requested to miniaturize the filter more and more, and are also requested to mount elements of the filter on a single plane. In order to realize further miniaturization of the filter without spoiling the electrical characteristics thereof, it is necessary to develop a new dielectric material. Furthermore, many recent communication devices have been used in higher frequencies. One example thereof is that demand for filters operable in a frequency band more than about 1.5 GHz has increased. The 1.5 GHz band corresponds to the frequency band for data communication using satellites e.g., filters used in a mobile navigation system (1.6 GHz band) or in satellite communication (1.5 GHz).


PROBLEM TO BE SOLVED BY THE INVENTION

However, the bandpass filters with the above-mentioned structure, particularly in case o

REFERENCES:
patent: 3135935 (1964-06-01), Engelbrecht
patent: 4801905 (1989-01-01), Becker
patent: 4916417 (1990-04-01), Ishikawa et al.
Matsunaga et al., "Electromagnetic Coupling Between Two-layered Microstrip lines", Mitsubishi Elec. Corp. Sep. 15, 1990, p. 2-397.

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