Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1991-03-07
1993-08-10
Pascal, Robert J.
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333234, H01P 1203, H01P 130
Patent
active
052352986
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a temperature compensated microwave stripline filter which may be used as a band-pass filter for a microwave range for example.
BACKGROUND ART
There is known a microwave stripline filter in which it comprises a pair of dielectric ceramic substrates between which one or more resonator conductors are disposed in a predetermined pattern to form a resonator. In such a microwave stripline filter, one or more resonator conductors having a length corresponding to a predetermined resonant frequency are provided on each of the opposite inner surfaces of the paired dielectric ceramic substrates, a ground conductor is provided on the outer surface of the each dielectric ceramic substrate, and the dielectric ceramic substrates are superimposed and fixed to each other so that the resonator conductors provided on the inner surfaces thereof are integrally connected to each other. Such a stripline filter for microwaves is disclosed in U.S. Pat. Nos. 4,157,517 and 4,266,206 for example. Similar stripline filters can also be found in U.S. Pat. No. 4,785,271 and Japanese Patent Prepublication No. 62-263702.
With the microwave stripline filter of the abovementioned type, generally, each dielectric ceramic substrate is made of ceramic material such as BaO-TiO.sub.2, BaO-TiO.sub.2 -rare earth or the like.
However, there is disadvantage that the commonly used ceramic material has a resonant frequency which is decreased as the temperature is risen because the temperature coefficient of the resonant frequency is of a negative characteristic.
It is therefore an object of the present invention to provide a stripline filter for microwaves wherein the disadvantage in the conventional filter can be overcome, any variation in temperature which may occur during the operation of the filter can be compensated so as to reduce the variation of a resonant frequency.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a microwave stripline filter having a pair of dielectric substrates which are stacked to each other, each substrate being provided with a ground electrode on the outer surface and if necessary on the peripheral surface thereof, and resonant electrodes which are positioned between the stacked surfaces of the substrates and have a predetermined pattern, characterized in that one of the dielectric substrates is formed by ceramic material having a negative temperature coefficient of resonant frequency, and the other substrate is formed by a ceramic material having a positive temperature coefficient of resonant frequency.
The paired dielectric substrates may be constructed by a combination of materials which have same composition but the negative temperature coefficient and the positive temperature coefficient, respectively.
Alternatively, the paired dielectric substrates may be constructed by a combination of materials which have different compositions, and the negative temperature coefficient and the positive temperature coefficient, respectively.
In the thus constructed microwave stripline filter according to the present invention, the paired dielectric substrates have reverse resonant frequency-temperature characteristices, respectively, and as a result, any variations of the resonant frequency in the respective substrates, which may occur at any variation in temperature during the operation of the filter, can be compensated with each other. Therefore, the filter can be stably operated without any influence of the variation in temperature.
BRIEF DESCRIPTION OF DRAWINGS
In the accompanied drawings:
FIG. 1 is a perspective view showing a completed microwave stripline filter according to one embodiment of the present invention;
FIG. 2 is an exploded perspective view showing a pair of dielectric substrates which form the stripline filter shown in FIG. 1; and
FIG. 3 is a graph of a temperature characteristic showing how the temperature coefficient of resonant frequency in the stripline filter according to present invention may be changed by the var
REFERENCES:
patent: Re31470 (1983-12-01), Bedand et al.
patent: 3798578 (1974-03-01), Konishi et al.
patent: 3840828 (1974-10-01), Linn et al.
patent: 4940955 (1990-07-01), Higgins, Jr.
Banno Hisao
Nishiki Masahiro
Ham Seung
NGK Spark Plug Co. Ltd.
Pascal Robert J.
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