MICROWAVE CIRCUIT

Abstract: A microwave circuit in which a first metallic case (1, 10), which has on the end face of a cylindrical microwave transmission line a ring-like protruding part (3, 11), is in contact with a second metallic case (4) having a plane-like shape. Since, only in the narrow region of the protruding part (3, 11), it is reliably in contact with the second plane-like metallic case (4), the satisfactory electromagnetic contact between the cases is obtained, and desirable characteristics can be secured.

Description: The present invention relates to a microwave circuit used in a microwave communication apparatus, a satellite broadcast receiving converter or the like. Recently, there have been remarkable developments in microwave devices used in microwave communication apparatuses, and it is easy to procure low-noise devices such as HEMT and MES-FET, so that the noise factor in reception-type low-noise converters, in particular, is decreasing year after year. However, even if the low-noise microwave device itself exhibits a satisfactory noise factor, the loss and impedance mismatching between the input section and the microwave device have a significant influence, making it impossible, in some cases, to obtain a desired noise factor for the low-noise converter as a whole. Such a conventional microwave circuit will be described with reference to the drawings. Fig. 3 shows a short-circuit section of a conventional cylindrical waveguide, and Fig. 4 is a sectional view of the same. In Fig. 3, numeral 1 indicates a metal body including a cylindrical waveguide 5, and numeral 2 indicates a mounting surface for a short-circuit plate 4. Usually, the short-circuit plate 4 is fixed to the mounting surface 2 by means of screws or the like to form a short-circuit plane. If the short-circuit plate 4 is in an ideal short-circuit state, a microwave being propagated through the cylindrical waveguide 5 makes a total reflection to change direction of propagation without involving any loss. In the above-described construction, however, an adequate contact cannot be attained, in particular, at an end of the cylindrical waveguide due to a variation in the surface precision of the mounting plate 2 and in the flatness of the short-circuit plate 4, with the result that the short-circuit plate 4 does not function as a perfect short-circuit plane. Thus, when using the short-circuit plane of a low-noise converter, the input power cannot be reflected adequately, resulting in deterioration in noise factor and input VSWR. A similar problem is encountered in cylindrical waveguide/microstrip-line (CWG/MSL) conversion sections where poor contact between conductors of a coaxial line can lead to a deterioration in the VSWR. It is known from JP-A-2-183601 to provide a microwave circuit in which a metal body acting as an external conductor of a coaxial line has a concentric circle-like prominence formed on a contact surface thereof to provide a means for forming an adequate contact between the metal body and a ground plane of a microstrip line (MSL). If, however, an adequate contact is not achieved it may be necessary to replace the whole metal body. It is known from EP-A1-0498896 to provide a microwave circuit which includes a metal body having a cylindrical-waveguide, a contact surface and a bore extending from said cylindrical-waveguide to said surface. The metal body serves as an external conductor of a coaxial line. A hollow dielectric supporter is fitted within said bore and a conductor which serves as an internal conductor of the coaxial line extends through said hollow dielectric supporter, and projects into said cylindrical-waveguide. The conductor also extends through a hollow metal supporter also fitted in the bore. The bore has a small diameter bore part and a large diameter bore part, with said hollow dielectric supporter being fitted within the small diameter bore part and the hollow metal supporter being fitted in said large diameter bore part. The hollow metal supporter is such that it projects from the surface of the metal body so as to make positive contact with a ground plane of a dielectric substrate, whereby an adequate contact is made between the metal body and said ground plane. EP-A1-0498896 constitutes a part of the state of the art in accordance with Article 54(3) EPC. JP-A-2-183601 and EP-A1-0498896 both describe means for improving contact between an external conductor of a coaxial line and a ground plane of a CWG/MSL. It is an object of the present invention to provide a microwave circuit in which an adequate contact is ensured between external conductors comprising conduction sections of a coaxial line. To achieve the above object, the microwave circuit of the present invention comprises: a metal body having a cylindrical-waveguide, a contact surface and a bore extending from said cylindrical-waveguide to said surface, said metal body serving as an external conductor of a coaxial line; a dielectric substrate laid on said metal body; a dielectric supporter fitted within said bore; and a conductor which serves as an internal conductor of the coaxial line extending through said dielectric supporter and which projects into said cylindrical-waveguide, characterised in that said conductor also extends through a metal supporter also fitted in the bore, said metal supporter and said metal body comprising conductor sections of said coaxial line, and said bore has a small diameter bore part and a large diameter bore part, said dielectric supporter being fitted within the small diameter bore part and the metal supporter being fitted in said large diameter bore part, and a concentric-circle-like prominence is provided on either the metal body or the metal supporter which, in use, are brought into contact with each other, whereby an adequate contact is made between the metal supporter and the metal body comprising the conductor sections of the coaxial line. Due to the above construction of the present invention, the metal body is held in contact with the metal supporter solely through a small region corresponding to the prominence provided on either of the metal body or the metal supporter, thereby attaining an adequate electromagnetic contact between the two metal bodies and ensuring satisfactory characteristics. The features of the invention will be better understood from the following description of embodiments with reference to the drawings, of which:- Figs. 1 and 2 are sectional views of cylindrical-waveguide/microstrip-line (CWG/MSL) conversion sections according to first and second embodiments of the present invention; Fig. 3 is an exploded perspective view of a short-circuit section of a conventional cylindrical waveguide; and Fig. 4 is a sectional view of the same. First and second embodiments of the present invention will be described with reference to the drawings. Figs. 1 and 2 show a sectional view of cylindrical-waveguide/microstrip-line conversion sections in a short circuit section of a cylindrical waveguide. Numeral 10 indicates a metal body including a cylindrical waveguide; numeral 6 indicates a post member; numeral 7 indicates an MIC substrate having a microstrip line; numeral 8 indicates a metal supporter for forming a hollow coaxial line-together with the post member 6; and numeral 9 indicates a dielectric supporter forming a dielectric coaxial line with the post member 6. In Figs. 1 and 2, a microwave propagated through the cylindrical waveguide in a direction perpendicular to the plane of the drawings is converted to a coaxial mode in the section of the post member 6 and propagated through coaxial lines formed by the components 9 and 8, and mode conversion is further effected in the connection section between the MIC substrate 7 and the post member 6 to propagate the microwave through the microstrip line on the MIC substrate 7. If, in the above waveguide/microstrip-line conversion section, the contact between the metal spacer 8 and the metal body 10 is not adequate, discontinuous portions are present in external conductors in the coaxial lines formed by the metal spacer 8 and the dielectric supporter 9, thereby causing a loss and deterioration in VSWR during microwave propagation. In view of this, a concentric-circle-like prominence 11 is provided on the side of the metal body 10, in the case of Fig. 5, and on the side of the metal support 8, in the case of Fig. 6, thereby an adequate contact is attained in the external conductor sections of the two coaxial lines mentioned above, thus ensuring satisfactory propagating characteristics. Thus, in accordance with the present invention, a concentric-circle-like prominence is provided on the external conductor forming one coaxial line, and brought into contact with the external conductor of the other coaxial line, thereby preventing loss and deterioration in VSWR due to the generation of discontinuous portions in the coaxial external conductors.

Claims: A microwave circuit comprising: a metal body (10) having a cylindrical-waveguide (5), a contact surface and a bore extending from said cylindrical-waveguide (5) to said surface, said metal body (10) serving as an external conductor of a coaxial line; a dielectric substrate (7) laid on said metal body (10); a dielectric supporter (9) fitted within said bore; and a conductor (6) which serves as an internal conductor of the coaxial line extending through said dielectric supporter (9) and which projects into said cylindrical-waveguide (5), characterised in that said conductor (6) also extends through a metal supporter (8) also fitted in the bore, said metal supporter (8) and said metal body (10) comprising conductor sections of said coaxial line, and said bore has a small diameter bore part and a large diameter bore part, said dielectric supporter (9) being fitted within the small diameter bore part and the metal supporter (8) being fitted in said large diameter bore part, and a concentric-circle-like prominence (11) is provided on either the metal body (10) or the metal supporter (8) which, in use, are brought into contact with each other, whereby an adequate contact is made between the metal supporter (8) and the metal body (10) comprising the conductor sections of the coaxial line. A microwave circuit as claimed in claim 1, characterised in that said conductor (6) serving as said internal conductor is a post (6).

Inventors: DEKI AKIHITO, KASHIMA YUKIRO, YOSHIMURA HIROKAZU, DEKI, AKIHITO, KASHIMA, YUKIRO, YOSHIMURA, HIROKAZU, DEKI, AKIHITO, 2-28-18, MINAMI TSUKAGUCHI-CHO, KASHIMA, YUKIRO, 1-7-10-501, TSUKAHARA, YOSHIMURA, HIROKAZU, 4-55-20, ANKOHJI-CHO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01P1
IPC codes: H01P5, H01P1, H01P11