Waveguide-microstrip transition

Abstract: A waveguide-microstripline transformer comprising a waveguide (6) which is closed at one end and has a slit (7) at a side wall thereof, a dielectric substrate (8) placed on the slit, a microstripline (9) placed on the dielectric substrate and a shield case (10) covering the dielectric substrate, whereby less blocking against the incident electromagnetic wave is attained.

Description: BACKGROUND OF THE INVENTION This invention relates to a waveguide-microstripline transition, which is used in a down converter etc. for broadcasting or communication by man-made satellites, and in which the mode of the electromagnetic wave is transformed from a mode to propagate in a waveguide to a mode to propagate in a microstripline. In recent years, satellite broadcasting became popular, and CS broadcastings using commercial communication satellite have begun their service, resulting in increased occasions for general housholds to receive broadcastings from plural satellites. In the course of this development, in addition to the demands for size and cost-reduction for the receiving antena, the interference of a polarized wave from a satellite with a differently polarized wave has arisen as a new problem. And it resulted in the renewed understanding of the importance of the low-noise down-converter with excellent performance, the ability of which for discriminating the cross polarization determines, when a parabola antena is used, the suppression of the interference. In the following, an explanation is made on a conventional waveguide-microstripline transition shown in Fig.3. Referring to Fig. 3, a conventional waveguide-microstripline transition comprises a cylindrical waveguide 1, a shield case 2, dielectric plate 3, and two microstriplines 4 and 5 working as probe. The shield case 2 or a short cylinder with a bottom plate has the inside diameter same as the waveguide 1 and the depth of 1/4 of the wave length and closes the end of the waveguide with a dielectric plate 3 in between. On the dielectric substrate 3, there are microstriplines 4 and 5. When an electromagnetic wave (assuming single polarized one) is propagated through the waveguide 1, it is totally reflected by the shield case 2, and the reflected wave excites the probe 4 to be transformed to an electromagnetic wave which propagates along the microstripline. If the incident electromagnetic waves are of cross polarized waves, provision of another probe 5 makes it possible to transform the waves with two polarized waves mutually orthogonal to waves on the microstriplines. However, in the above conventional structure it was necessary to make the waveguide 1 and the dielectric substrate perpendicular to each other. Accordingly, it had a problem that, when used in combination with a parabola reflector such as antena, the area to block the electromagnetic wave incident upon the reflector became large. It also had a problem that, when receiving cross polarized waves, the orthogonally polarized waves interferenced each other or the discrimination for them deteriorated, since two probes were formed on a same dielectric substrate placed at a section of the waveguide. A waveguide-microstripline transition in which a microstripline is provided on top of a dielectric substrate, which is located on a slit which is formed in a waveguide is disclosed in JP-A-4109702. An emitting/receiving device for orthogonal polarization comprising cavities shielding antennas which are provided in order to couple the waveguide to reception and emission circuits is disclosed in EP-A-0295688. SUMMARY OF THE INVENTION It is an object of the present invention to provide a waveguide-microstripline transition according to the preamble of claim 1 with less blocking and with excellent discrimination for cross polarized waves. This object is obtained with a waveguide-microstripline transition having the features of the characterizing portion of claim 1. To attain the above described object, the waveguide-microstripline transition for receiving single polarized waves according to the present invention comprises a waveguide having a slit at a side wall thereof, a dielectric substrate placed on the slit, a microstripline working as a probe on the dielectric substrate, and a shield case covering the dielectric substrate. It is to be noted that electromagnetic waves incident through the waveguide is transformed by passing through the slit to a mode to propagate through rectangular waveguide, and is transformed by being stopped and reflected by the shield case to a mode to propagate along the microstripline. With the probe placed on the side wall of the waveguide, the blocking is reduced considerably, and the electromagnetic wave, after passing the slit, is reflected at the end of the shield case to be efficiently transformed to a wave propagating along the microstripline. If the waveguide is of circular cross section, the electromagnetic wave is efficiently transformed to the shield case by arranging the direction of the longer sides parallel to the axis of the waveguide. According to further configuration of the invention, the dielectric substrate is provided, in addition to the above described probe of microstripline, with an earthing conductor on the backside thereof, connected with the waveguide and the shield case, simplifying the provision and earthing of the shield case. Also, the rectangular form of the shield case makes the total reflection of the electromagnetic wave under rectangular-waveguide propagation mode by the end of the shield case sure and efficient. For receiving cross polarized waves, the waveguide-microstripline transition, according to the present inyention, is provided, in addition to the structure described above, with a conductor bar piercing through a hole in a side wall with a dielectric ring between them, and with a metal plate in the waveguide between the probe and the conductor bar, which is conected with a second microstripline also formed on the dielectric substrate, the metal plate being parallel to the line through the probe and the conductor bar. With such structure, waves consisting of two orthogonally polarized waves are separated by the metal plate, and each polarized wave individually excites the stripline and the conductive bar, resulting in reliable separation and favourable discrimination of cross polarized waves. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(a) is an exploded perspective view of a waveguide-microstripline transition showing the first embodiment of the present invention. Fig. 1(b) is a side section of the waveguide-microstripline transition showing the first embodiment of the present invention. Fig. 2(a) is an exploded perspective view of a waveguide-microstripline transition showing the second embodiment of the present invention. Fig.2(b) is a side section of the waveguide-microstripline transition showing the second embodiment of the present invention. Fig.3(a) is a plan view of a conventional waveguide-microstripline transition for single polarized wave receiving. Fig.3(b) is a side section of the conventional waveguide-microstripline transition for single polarized wave receiving. Fig.3(c) is a plan view of another conventional waveguide-microstripline transition for cross polarized wave receiving. Fig.3(d) is a side section of the conventional waveguide-microstripline transition for cross polarized wave receiving. DETAILED DESCRIPTION OF THE INVENTION Embodiment 1 Referring to Fig. 1, a waveguide-microstripline transition according to the present invention comprises a cylindrical waveguide 6 with circular inside cross section and with metal wall at the one end and with a rectangular slit 7 at a side wall. It is provided on the side wall with a dielectric substrate 8, on which a microstripline 9 to function as a probe is placed. The substrate 8 is covered with a shield case 10 soldered with the substrate by way of copper foil 11, and is further provided with an earth conductor on the surface opposite to the case. The case and the copper foil is connected with the earth conductor through the holes 12 on the foil. When an electromagnetic wave arrives through the opening of the waveguide, it is totally reflected by the metal wall at the end of the waveguide, transformed by the slit 7 from the mode propagating in a circular waveguide to the mode propagating in a rectangular waveguide to proceed into the shield case 10 forming a rectangular waveguide, where the wave is again totally reflected by the metal end wall, and, by exciting the stripline 9 as a probe, is transformed to an wave to propagate along the microstripline. Numerically, for the waves ranging from 11 GHz to 12 GHz, the slit 7 was preferably 1 mm depth, 15 mm length (along the cylinder axis), and 2 to 3 mm width, and the shield case 10 to act as the end of a rectangular waveguide had the opening of 20 mm × 5 to 6 mm and depth of 5 mm. According to the transition of the present embodiment, quite favourable transformation was attained without making the waveguide 6 and the dielectric substrate 8 perpendicular to each other, and, when used combined with a reflector of parabolic form, effect by blocking is considerably reduced. Embodiment 2 Referring now to Fig.2, another waveguide-microstripline transition according to the present invention comprises a cylindrical waveguide 13 closed at the end with a metal wall and having a rectangular slit 14 at a side thereof. It is provided on the side wall with a dielectric substrate 15 on which a first stripline 16 to work as a probe is placed. The substrate 15 is covered with a shield case 17 soldered with the substrate by way of copper foil 18. The shield case 17 and the foil 18 are connected electrically with the earth conductor on the back of the substrate through the holes 19 on the foil 18. The waveguide is further provided with an electrically conductor bar 22 and a metal plate 25. The bar 22 is inserted into the waveguide for a certain length through a hole 20 and supported by an insulator ring 21 in between the hole 20. The bar 22 is soldered with a second stripline 24 deposited on the substrate 15 at a hole 23 of the second stripline 24. The metal plate 25 is placed between the stripline 16 as a probe and the bar 22 in the waveguide 13, the main surface of the plate 25 being parallel with the line which passes the probe 16 and the bar 22. When electromagnetic waves consisting of two polarized waves - a wave with the electric field component of X axis direction (EX), and a wave with the electric field component of Y axis direction (EY) - enter the waveguide 13, the EY component is totally reflected by the metal plate 25, excites the conductive bar 22, and is transformed to an electromagnetic wave which propagates along the second microstripline 24, while, the EX component, passing without being reflected by the metal plate 25, is reflected totally by the metal end plate of the wave guide, and is transformed to an electromagnetic wave which propagates along the microstripline as explained for the Embodiment 1. Thus, according to this embodiment, a waveguide-microstripline transformer is obtained which has considerably reduced blocking-effect as Embodiment 1, and separation of two orthogonally polarized waves with excellent discrimination by exciting the probe 16 and the conductor bar 22 at different places in the guide with the cross-polarized electromagnetic wave, separating them with the metal plate 25. In Embodiment 1, the shield case 10 can be fastened to the substrate 8 by a screw instead of soldering. Also, the shield case 10 may be such a structure as the side wall part of the case is formed as one body as the waveguide 6 proper and a metal end plate is fastened thereupon by a screw for example, and these structure may be applied for the transition of the Embodiment 2. Further, the cross section of the inside wall of the waveguide 6 is not confined to circular form. It may be elliptic, rectangular or of any other form. Thus, according to the present invention, an excellent waveguide-microstripline transition is obtained, comprising a waveguide, a slit on a wall thereof, a dielectric substrate thereon, a probe of microstripline thereon, and a shield case covering it, and resulting in the possible arrangement of the dielectric substrate parallel to the incoming direction of the electromagnetic wave and in the considerable reducing of blocking effect which has been an obstacle when used with reflectors of such a type as parabola. Also, a waveguide-microstripline transition for receiving a cross polarized wave with excellent discrimination can be realized by providing the above described structure with a transition structure consisting of a conductive bar, dielectric ring therearound, and microstripline soldered at the outer end thereof, and with a metal plate to separate the orthogonally polarized waves.

Claims: A waveguide-microstripline transition comprising a circular waveguide (1,6,13) which is closed at one end thereof and has a slit (7,14) at a side wall thereof, a dielectric substrate (8,15) placed on said slit (7,14), and a first microstripline probe (9,16) placed on said dielectric substrate (8,15), characterized by a shield case (10,17) forming a rectangular waveguide covering the microstripline probe (9,16) on said dielectric substrate (8,15), A waveguide-microstripline transition according to claim 1, characterized by a conducting bar (22) penetrating the sidewall of said waveguide (13) through a hole (20) and being supported thereby via a dielectric ring (21) surrounding said bar (22), a second microstripline (24) connected with said conducting bar (22), and a metal plate (25) which is placed in said waveguide (13) between said first microstripline ( 16) and said conducting bar (22) and is parallel with said conducting bar (22). The waveguide-microstripline transition of claim 2, wherein said hole (20) is placed at the same side wall as said wall having said slit (13). The waveguide-microstripline transition of claim 2, wherein said metal plate (25) is arranged in parallel with the line passing through said conducting bar (22) and said slit (13). The waveguide-microstripline transition of one of the preceding claims, wherein said waveguide (6,13) has a circular inside cross-section, and said slit (7,14) being parallel to the axis of said waveguide (6,13). The waveguide-microstripline transition of one of the preceding claims, wherein said dielectric substrate (8,15) is provided with an earth conductor connected with said waveguide (6,13) on the surface opposite to that of said first microstripline probe (9,16). The waveguide-microstripline transition of claim 6, wherein said dielectric substrate (8,15) is provided with a conductive foil (11,18) on the same surface as said first microstripline probe (9,16) connected with said earth conductor through a hole in said dielectric substrate (8,15). The waveguide-microstripline transition of one of the preceding claims, wherein said shield case (10,17) has a rectangular cross-section.

Inventors: KASHIMA YUKIRO, KINOSHITA AKIRA, YOSHIMURA YOSHIKAZU, KASHIMA, YUKIRO, KINOSHITA, AKIRA, YOSHIMURA, YOSHIKAZU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H01P1
IPC codes: H01P5, H01P1