MICROWAVE CIRCUIT

Abstract: A conductive strip (1) of an MSL is connected with the internal conductor of a coaxial line provided with a metallic case (3) as its external conductor, via a through hole (9) bored in a dielectric substrate (2) from an MSL grounding surface (11) which is provided on the dielectric substate (2). A ring-like protruding part (7) is formed on the metallic case and is in contact with the grounding surface (11). Thereby, the external conductor of the coaxial line is reliably in contact with the MSL grounding surface (11). Since there is no mismatching part, the loss and the deterioration of VSWR in the MSL converting part and the coaxial line can be prevented, and desirable characteristics are obtained.

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 (hereinafter referred to simply as "CWG") - MSL conversion section; Fig. 4 is a sectional view of the same; Fig. 5 is an enlarged view of a dielectric substrate forming an MSL; and Fig. 6 is a reverse-side view of the same. In Figs. 3 to 6, numeral 1 indicates a conductor strip of the MSL; numeral 2 indicates a dielectric substrate; numeral 3 indicates a metal body having a CWG 4; numeral 5 indicates a post; numeral 6 indicates a Teflon supporter; numeral 9 indicates a through-hole for connecting the conductor strip 1 with the post 5; and numeral 11 indicates a ground plane of the dielectric substrate 2. The operation of the microwave circuit, constructed as described above, will be explained. First, in Figs. 3 and 4, a microwave propagated through the CWG 4 is converted to a coaxial-line mode in the section of the post 5, and propagated through the coaxial line using the Teflon supporter 6 as an internal dielectric. Next, in Figs. 5 and 6, the microwave propagated through the coaxial line is mode-converted by a matching pattern 10 provided in the ground plane 11 of the dielectric substrate 2 to an MSL having the same characteristic impedance as the coaxial line without involving any deterioration in characteristics. Then, the post 5, which constitutes the central conductor of the coaxial line, is connected to the conductor strip 1 through the through-hole 9. In the above-described construction, however, a sufficient contact may not be attained between the portion of the ground plane around the matching pattern 10 of the dielectric substrate 2 and the metal body 3 due to a warp in the dielectric substrate 2 or an inadequate flatness of the metal body 3. In such a case, the characteristic impedance of the coaxial line differs from that of the MSL, and mismatching is caused, resulting in deterioration in 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 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. The present invention also provides means for forming an adequate contact between a metal body of a microwave circuit and a ground plane of a microstrip line (MSL). It does this by providing a hollow metal supporter which fits in a bore of the metal body and projects from a contact surface of the body. Accordingly, the present invention provides a microwave circuit comprising: 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; a conductor strip of a microstrip line (MSL) laid on said dielectric substrate on a surface thereof opposite to a ground plane of the microstrip line (MSL) and having a through-hole; a hollow dielectric supporter fitted within said bore; and a conductor which serves as an internal conductor of the coaxial line connected to said conductor strip and extending through said through-hole, a through-hole formed in said dielectric substrate and said hollow dielectric support, and which projects into said cylindrical-waveguide, characterised in that said conductor also extends through a hollow metal supporter also fitted in the bore, and said bore has a small diameter bore part and a large diameter bore part, 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, said hollow metal supporter being such that it projects from the surface of the metal body so as to make positive contact with the ground plane of the dielectric substrate, whereby an adequate contact is made between said metal body and said ground plane of said microstrip line (MSL). Due to the above construction of the present invention, the coaxial-line-external-conductor section on the side of the metal body is positively held in contact with the ground plane of the MSL by virtue of the hollow metal supporter, so that no mismatching is involved and it is possible to prevent deterioration in VSWR in the coaxial-line/MSL conversion section, thereby ensuring satisfactory characteristics. The features of the present invention will be more readily understood from the following description with reference to the drawings, of which: Fig. 1 is a perspective view of a CWG/MSL conversion section in an embodiment of the present invention; Fig. 2 is a sectional view of the same; Fig. 3 is a perspective view of a conventional CWG/MSL conversion section; Fig. 4 is a sectional view of the same; and Figs. 5 and 6 are an enlarged view and a reverse-side view respectively of a dielectric substrate forming an MSL. An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view of a CWG/MSL conversion section in an embodiment of the present invention, and Fig. 2 is a sectional view of the same. In Figs. 1 and 2, numeral 1 indicates a conductor strip of an MSL; numeral 2 indicates a dielectric substrate; numeral 3 indicates a metal body including a CWG 4; numeral 5 indicates a post; numeral 6 indicates a Teflon supporter; numeral 8 indicates a metal supporter; numeral 9 indicates a through-hole for connecting the conductor strip 1 with the post 5; and numeral 11 indicates a ground plane of the dielectric substrate 2. The operation of the microwave circuit, constructed as described above, will now be explained. First, a microwave being propagated through the CWG 4 is mode-converted in the section of the post 5 into a coaxial-line mode using the Teflon supporter 6 as an internal dielectric, and then into a hollow coaxial-line mode using the interior of the metal supporter 8 as an external conductor. Then, it is converted into an MSL having the same characteristic impedance as that of the two types of coaxial lines mentioned above. The section of the post 6 which has been passed through the through-hole is connected with the conductor strip 1. In this embodiment, the metal supporter 8 is made somewhat higher than the metal body 3, whereby it is possible to attain an adequate contact between the external conductor of the coaxial line and the ground plane of the MSL, thereby realising a perfect ground plane matching and preventing the generation of a mismatched portion with no influence by a warp of the dielectric substrate 2. Thus, in accordance with this embodiment, an appropriate height of the metal supporter 8 is selected, thereby realising a satisfactory coaxial-line/MSL conversion section involving no deterioration in VSWR. Thus, in accordance with the present invention, the hollow metal supporter projects from a contact surface which is on a side of a metal body serving as an external conductor of a coaxial line and which connects a conductor strip of a MSL formed on a dielectric substrate to an internal conductor of the coaxial line through a through-hole extending from the ground plane of the MSL through the dielectric substrate, whereby it is possible to realise a satisfactory coaxial-line/MSL conversion section involving no deterioration in VSWR, thus providing a remarkable advantage in terms of utility.

Claims: A microwave circuit comprising: a metal body (3) having a cylindrical-waveguide (4), a contact surface and a bore extending from said cylindrical-waveguide (4) to said surface, said metal body (3) serving as an external conductor of a coaxial line; a dielectric substrate (2) ; a conductor strip (1) of a microstrip line (MSL) laid on said dielectric substrate (2) on a surface thereof opposite to a ground plane (11) of the microstrip line (MSL) and having a through-hole (9); a hollow dielectric supporter (6) fitted within said bore; and a conductor (5) which serves as an internal conductor of the coaxial line connected to said conductor strip (1) and extending through said through-hole (9), a through-hole formed in said dielectric substrate (2) and said hollow dielectric support (6), and which projects into said cylindrical-waveguide (4), characterised in that said conductor (5) also extends through a hollow metal supporter (8) also fitted in the bore, and said bore has a small diameter bore part and a large diameter bore part, said hollow dielectric supporter (6) being fitted within the small diameter bore part and the hollow metal supporter (8) being fitted in said large diameter bore part, said hollow metal supporter being such that it projects from the surface of the metal body (3) so as to make positive contact with the ground plane (11) of the dielectric substrate (2), whereby an adequate contact is made between said metal body (3) and said ground plane (11) of said microstrip line (MSL). A microwave circuit as claimed in claim 1, characterised in that said conductor (5) serving as said internal conductor is a post (5).

Inventors: AONO SHOZO, DEKI AKIHITO, KASHIMA YUKIRO, KINOSHITA AKIRA, NISHIOKA KAZUYOSHI, SHIOMI YASUFUMI, AONO, SHOZO, DEKI, AKIHITO, KASHIMA, YUKIRO, KINOSHITA, AKIRA, NISHIOKA, KAZUYOSHI, SHIOMI, YASUFUMI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01P5
IPC codes: H01P5