Wave transmission lines and networks – Resonators – Cavity resonator
Patent
1993-09-08
1995-03-07
Ham, Seungsook
Wave transmission lines and networks
Resonators
Cavity resonator
333 26, 343700MS, H01P 706
Patent
active
053962028
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an assembly for coupling a microstrip circuit to a cavity resonator.
The invention is also directed to a method for coupling a microstrip circuit to a cavity resonator.
A cavity resonator has a structure which can be mathematically modelled as an LC resonant circuit. The dimensions of the cavity determine its resonant frequencies, several of which are possible depending on the principal dimensions of the cavity. The cavity resonator is excited by a transistor and a microstrip circuit connected to the transistor device.
According to conventional technology, microstrip circuits are used in conjunction with dielectric resonators up to 30 GHz frequency. Above this 30 GHz frequency the size of the resonator at high frequencies becomes so small that its Q (quality factor) deteriorates significantly. In addition, the size of the dielectric resonator becomes so small that the reliable placement of the resonator onto the microstrip circuit in mass production becomes extremely difficult.
Waveguide systems operating at millimeter wavelengths typically employ diode oscillators. These combinations are, however, clumsy and expensive.
Combinations of microstrip circuits with cavity resonators have been in use up to frequencies of several GHz, but in the millimeter wavelength range the typical coupling method based on a small probe antenna reaches its limits in terms of manufacturing possibilities.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the above described techniques and to achieve a novel type of assembly and method for coupling a microstrip circuit to a cavity resonator.
The invention is based on forming the coupling from the microstrip to the cavity resonator by means of a slot made in the ground plane and a planar radiator disposed on the surface of a coupling piece made of a suitable dielectric material.
More specifically, the assembly according to the invention comprises a substrate plate, a microstrip circuit fabricated on one side of said substrate plate, a ground plane fabricated on the other side of said substrate plate, and a cavity resonator wherein the microstrip circuit is coupled to said cavity resonator by means of a slot fabricated in said ground plane and a planar radiator disposed between said ground plane and said cavity resonator.
Furthermore, the method according to the invention comprises the steps of fabricating a microstrip circuit on one side of a substrate plate, fabricating a ground plane on the other side of said substrate plate, fabricating a slot in said ground plane, coupling said microstrip circuit to a cavity resonator by means of said slot, and disposing a planar radiator between said ground plane and said cavity resonator.
The invention provides outstanding benefits.
The resonator according to the invention can be readily manufactured for frequencies in the range 1-100 GHz. The upper ground plane can be omitted from the design, because the planar radiator directs the radiating field toward the cavity resonator. Selection and/or attenuation of different resonant modes is easy to attain by altering the position and dimensions of the planar radiator with respect to the cavity resonator. Further, temperature compensation of the operating frequency can be readily implemented by suitable material choice of the planar radiator substrate with a compensating temperature coefficient of the dielectric constant .epsilon..sub.p.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
FIG. 1 shows an expanded view in perspective of the coupling circuit according to an embodiment of the invention between a microstrip circuit and a cavity resonator;
FIG. 2a shows a first alternative coupling coefficient of the circuit according to an embodiment of the invention
REFERENCES:
patent: 4211987 (1980-07-01), Pan
patent: 4903033 (1990-02-01), Tsao et al.
patent: 4937585 (1990-06-01), Shoemaker
Ham Seungsook
Valtion teknillinen tutkimuskeskus
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