Microwave stripline resonators

Abstract: This invention relates to a compact and high performance microwave stripline resonator consisting of a dielectric substrate (1) provided with a strip electrode (5) and a depression (4) coated with an electrode (4a) which is connected to an end of said strip electrode provided on one of the surfaces (2) of said dielectric substrate and a grounding electrode (3) provided on the other surface of said dielectric substrate, and said grounding electrode is connected to the other end of said strip electrode. With this dielectric resonator construction, the characteristic impedance of said strip electrode and the characteristic impedance of said electrode coated on said depression are made different. As a result of this, the length of microwave strip line can be shortened without sacrificing the Q of the resonator. This is highly effective to realize compact resonators.

Description: This invention relates to microwave stripline resonators according to the preamble part of claim 1. Such resonators may be employed in mobile communication equipment such as mobile telephones. In particular, a compact and high performance microwave stripline resonator is disclosed. JP-A-2067802 discloses to miniaturize a matching circuit by forming matching stubs in a recessed part of a dielectric substrate. The recessed parts are not formed at freely chosen locations on either surface of the substrate. JP-A-2060303 is concerned with adjusting an electrical length of a microstrip line to obtain an optimum resonance frequency by punching parts at the tip of the microstrip line. JP-A-1226201 discloses a split ring resonator on which a capacity adjustment is attained by connecting the transmitting line of both open edges in a loop dielectric by means of capacities. Conventionally, a capacity element is attached to the transmitting line. This document discloses to eliminate the capacity element by providing a notch part at the bottom of the transmitting line in the dielectric and to provide an electrode in the notch part thereby generating capacities. GB-A-1442383 discloses a stripline waveguide mounted on an insulating substrate having a conductive back coating. A sub-resonator branches from the stripline thereby forming a T-junction. A trough is formed in the substrate which is not coated with an electrode. Such structure improves the performance of stripline components with open circuit terminations and reduces unwanted coupling between such stripline components and other circuit elements mounted on the same substrate. As shown in Figure 5, a conventional microwave stripline resonator consists of a strip electrode 6B provided on a surface of dielectric substrate 1 and a grounding electrode 3 provided on the reverse surface of said dielectric substrate 1. The strip electrode and the grounding electrode are interconnected. With such a construction of a conventional resonator, the length of strip electrode 6B is exclusively determined only by its frequency. Therefore, the employment of dielectric substrate 1 having a larger dielectric constant is desirable to make the resonator more compact. However, a dielectric substrate having a larger dielectric constant is generally associated with a lower no-load Q and an irregular flatness of temperature coefficient characteristics. Thus, a dielectric substrate having a large dielectric constant exhibits poor resonator characteristics. The present invention solves the problems associated with conventional stripline resonators, while offering compact and high-performance microwave stripline resonators. A microwave stripline resonator in accordance with the present invention comprises the features of claim 1. With this dielectric resonator construction, the characteristic impedance of the strip electrode and the characteristic impedance of the electrode which is coated on the depression are made different. As a result of this, the length of the microwave strip line can be shortened without sacrificing the Q of the resonator. This is highly effective to realize compact resonators. For a more complete understanding of the nature, features and advantages of the present invention, provided below is a detailed description of exemplary illustrative embodiments of the invention, which are illustrated by and best understood with reference to the accompanying drawings wherein: Figs 1(a) and 1(b) show respectively perspective and cross-sectional schematic views of an embodiment of microwave stripline resonators of the invention, Figs. 2 and 3 show perspective schematic views of microwave stripline resonators of other embodiments of the invention, Fig. 4 shows a perspective schematic view of filter device employing a microwave stripline resonator of the invention, and Fig. 5 shows a perspective view of conventional microwave stripline resonator. As shown in Fig. 1, in which one of the embodiments of the present invention is illustrated, adjacent surfaces of a rectangular dielectric substrate 1 are covered by a grounding electrode 3. A surface 2 of dielectric substrate 1 is provided with a depression 4 which is covered by an electrode 4A. Electrode 4A is connected to grounding electrode 3 through a strip electrode 5. Strip electrode 5 has a width identical to that of electrode 4A. With this stripline resonator construction, the total length of strip electrode 5 and electrode 4A covering depression 4 can be substantially shorter than the length of a stripline electrode of a conventional microwave stripline resonator. Fig. 2 shows another embodiment of the present invention, where the electrode length is made still shorter than that of the microwave stripline resonators shown in Fig. 1. This is accomplished by employing an electrode 6A which covers depression 4. Electrode 6A has a wider width than that of strip electrode 5 provided on the surface of dielectric substrate 1. Fig. 3 shows still another embodiment of the present invention providing a depression 7 which is covered by an electrode 7A with a U-shaped opening partly accommodating strip electrode 5. A filter device, employing the microwave stripline resonator shown in Fig. 1, is illustrated in Fig. 4 wherein adjacent surfaces of rectangular dielectric substrate 1 (not including surface 2) are covered by a grounding electrode 3 by means of metallization or such, and two rectangular depressions 4 are provided on the surface 2 of said dielectric substrate 1. Electrodes 4A covering depressions 4 are connected to grounding electrode 3. Signal output electrodes 9 are also provided on regions corresponding to depressions 4 on the rear side 8 of dielectric substrate 1. According to the resonator construction of the present invention, a compact and high-performance microwave stripline resonator can be realized by providing depressions covered by electrodes and strip electrodes connected thereto on a dielectric substrate.

Claims: A microwave stripline resonator comprising: a rectangular dielectric substrate (1) having a depression (4) on a first surface (2) of the substrate; a strip electrode (5) provided on said first surface (2) of said dielectric substrate (1); a grounding electrode (3) provided on a second surface of said dielectric substrate (1); an electrode (4A,6A,7A) coating said depression (4), characterized in that the depression (4) is arranged at a first end of said strip electrode (5) and said grounding electrode (3) is arranged at a second end of said strip electrode (5) and in that said electrode (4A,6A,7A) coating the depression (4) and said grounding electrode (3) connect the first and second end of said strip electrode (3) respectively, such that the impedance of the strip electrode (5) and that of the electrode (4A,6A,7A) coating the depression (4) is made different. A microwave stripline resonator according to claim 1, wherein the width of said depression (4) is wider that the width of said strip electrode (5). A microwave stripline resonator according to claims 1 or 2, wherein said depression (4) is U-shaped to partly accommodate said strip electrode (5).

Inventors: AIZAWA KIMIO, KITA MASAKI, AIZAWA,KIMIO, KITA,MASAKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01P7
IPC codes: H01P7