Hermetically sealed structure for joining two waveguides

Abstract: A first circular waveguide or an elliptical waveguide has an inner circumferential surface tapered such that its inside dimension is gradually reduced continuously toward an end thereof. The elliptical waveguide comprises an antenna waveguide connected to an antenna device. Another circular waveguide has an end joined to the end of the first circular waveguide or the elliptical waveguide. Both waveguides have different inside dimensions at the joined ends. A hermetic seal is sandwiched between the joined ends of both the waveguides. The tapered inner circumferential surface is effective to cancel out a susceptance produced by the hermetic seal. The first waveguide with the tapered inner circumferential surface can easily be manufactured by die casting.

Description: The present invention relates to a hermetically sealed structure for a junction between two waveguides, e.g., a feeder waveguide and an antenna waveguide, in a microwave circuit. Conventional hermetically sealed structures for a junction between two circular waveguides will be described below with reference to Figs. 1(a), 1(b) and 2(a), 2(b) of the accompanying drawings. Fig. 1(a) and Fig. 2(a) are transverse cross-sectional views and Fig. 1(b) and Fig. 2(b) are fragmentary longitudinal cross-sectional views. Figs. 1(a) and 1(b) show a conventional hermetically sealed structure for a junction between two circular waveguides. As shown in Figs. 1(a) and 1(b), a circular waveguide 1 has an end coupled to an end of another circular waveguide 2 by a junction having a disk-shaped hermetic seal 3 sandwiched between the coupled ends of the circular waveguides 1, 2. The junction also includes an annular gasket 4 placed in an annular groove which is defined in the end of the circular waveguide 2, and hermetically held against the hermetic seal 3. The circular waveguide 1 may serve as an antenna waveguide connected to an antenna device, and the circular waveguide 2 as a feeder waveguide connected to a radio transmitter/receiver device. In order to cancel out a susceptance produced by the hermetic seal 3 and achieve an impedance match at the junction, the circular waveguide 1 has a susceptance correction ring 5 projecting radially inwardly at the joined end thereof near to the hermetic seal 3. Figs. 2(a) and 2(b) show another conventional hermetically sealed structure for use at a junction between two circular waveguides. Those parts shown in Figs. 2(a) and 2(b) which are similar to those shown in Figs. 1(a) and 1(b) are denoted by the same reference numerals. The conventional hermetically sealed structure shown in Figs. 2(a) and 2(b) differs from the conventional hermetically sealed structure shown in Figs. 1(a) and 1(b) in that susceptance correction screws 6 are mounted in suitable locations on an inner circumferential wall surface of the circular waveguide 1 near the hermetic seal 3. The conventional hermetically sealed structure shown in Figs. 1(a) and 1(b) is complex in structure and expensive to manufacture because of the susceptance correction ring 5 on the circular waveguide 1. With the conventional hermetically sealed structure shown in Figs. 2(a) and 2(b), it is necessary to insert and adjust the susceptance correction screws 6 after the circular waveguide 1 is assembled. If the circular waveguides 1, 2 are used outdoors, then the hermetically sealed structure needs to have a certain drip-resistant structure. Furthermore, if an antenna coupled to the circular waveguide 1 employs two-frequency cross polarization, then since corrective quantities for the respective polarization components are different from each other, the conventional hermetically sealed structures are more complex in structure. It is a feature of an arrangement to be described below, by way of example, that it provides a hermetically sealed structure of very simple construction for a junction between two circular waveguides, or a junction between an elliptical waveguide and a circular waveguide, in which any mismatch of the impedance at the junction, caused by the susceptance of the hermetic seal, can be minimised or cancelled comparatively easily. In a particular arrangement to be described below, by way of example, there is a hermetically sealed structure for a junction between two circular waveguides in which a hermetic seal is sandwiched between the respective ends of the two circular waveguides, which includes a first circular waveguide having an inside diameter which is gradually reduced continuously towards an end thereof, which end is to be joined to an end of a second circular waveguide; and a second circular waveguide having an end to be joined to the end of the first circular waveguide; the first circular waveguide and the second circular waveguide having different inside diameters at the ends which are to be joined via the hermetic seal. One of the first and second circular waveguides may be an antenna waveguide connected to an antenna device, and the other of the first and second circular waveguides may be a feeder waveguide connected to a radio transmitter/receiver device. In another hermetically sealed structure or a junction between an elliptical waveguide and a circular waveguide, in which a hermetic seal is sandwiched between the respective ends of the elliptical waveguide and the circular waveguide, and which is to be described below, by way of example, there is an elliptical waveguide having an inside dimension which is gradually reduced continuously, the similarity of its shape being kept, towards an end thereof, which end is to be joined to an end of a circular waveguide; and a circular waveguide having an end to be joined to the end of the elliptical waveguide; the elliptical waveguide and the circular waveguide having different inside dimensions at the ends which are to be joined via the hermetic seal. The elliptical waveguide may be an antenna waveguide for connection to an antenna device, and the circular waveguide may be a feeder waveguide for connection to a radio transmitter/receiver device. Both the first circular waveguide of the first arrangement and the elliptical waveguide of the second arrangement each have a tapered inner circumferential surface such that the inside dimension of each is gradually reduced continuously toward the respective end thereof. The tapered inner circumferential surface is effective to minimise any susceptance produced by the hermetic seal. The following description and drawings disclose, by means of examples, the invention which is characterised in the appended claims whose terms determine the extent of the protection conferred hereby. In the following drawings:- Fig. 3(a) is a transverse cross-sectional view of a hermetically sealed structure for a junction between two circular waveguides, the view being taken along line A-A of Fig. 3(b); Fig. 3(b) is a fragmentary longitudinal cross-sectional view of the hermetically sealed structure shown in Fig. 3(a); Fig. 4(a) is a transverse cross-sectional view of a hermetically sealed structure for a junction between an elliptical waveguide and a circular waveguide, the view being taken along line A-A of Fig. 4(b); and Fig. 4(b) is a fragmentary longitudinal cross-sectional view of the hermetically sealed structure shown in Fig. 4(a). As shown in Figs. 3(a) and 3(b), a circular waveguide 1 has an end coupled to an end of another circular waveguide 2 by a junction having a disk-shaped hermetic seal 3 sandwiched between the coupled ends of the circular waveguides 1, 2. The junction also includes an annular gasket 4 placed in an annular groove, which is defined in the end of the circular waveguide 2. The gasket 4 is held hermetically against the hermetic seal 3. The circular waveguide 1 serves as an antenna waveguide connected to an antenna device, and the circular waveguide 2 serves as a feeder waveguide connected to a radio transmitter/receiver device. The circular waveguide 1 has an inner circumferential wall surface 7 which is tapered axially such that its inside diameter is gradually reduced continuously in the axial direction toward the junction. At the junction, the inside diameter of the circular waveguide 1 is smaller than the inside diameter of the circular waveguide 2. The difference between the inside diameters of the circular waveguides 1, 2 is selected to minimise or even cancel out susceptance produced by the hermetic seal 3. Therefore, the tapered inner circumferential wall surface 7 of the circular waveguide 1 serves as a susceptance corrector. Figs. 4(a) and 4(b) show a hermetically sealed structure for a junction between an elliptical waveguide and a circular waveguide providing another embodiment illustrative of the present invention. In this case, the waveguide 1 has an elliptical inside shape and the waveguide 2 has a circular inner cross-section. Accordingly, the hermetically sealed structure shown in Figs. 4(a) and 4(b) differs from the hermetically sealed structure shown in Figs. 3(a) and 3(b) only in that the tapered inner circumferential wall surface 7 of the waveguide 1 provides an elliptical opening at the junction, as shown in Fig. 4(a). As shown in Figs. 3(a), 3(b) and 4(a), 4(b), the circular and the elliptical waveguide 1 each have different input and output end shapes, due to the tapered inner circumferential wall surface 7 thereof, and the dimensions of the circle and of the ellipse of the respective circular waveguides 1, 2 are each different from the other at the hermetic seal 3, making it possible to compensate for the susceptance produced by the hermetic seal 3. Since the inner circumferential wall surface 7 is tapered axially compared with the external dimensions of the waveguides, being gradually reduced continuously in the axial direction toward the junction, either of the circular or the elliptical waveguide 1 lends itself to being manufactured by die casting, and hence can be manufactured very inexpensively, irrespective of whether the waveguide 1 has a tapered circular inner section or a tapered elliptical inner section. With the arrangements of the embodiments shown above, the different input and output end shapes of the circular or elliptical waveguides 1, which are generated by the tapered inner circumferential wall surface 7 thereof, are utilized to compensate for the susceptance produced by the hermetic seal 3. Therefore, no extra members, such as a ring or screws, need to be added for susceptance correction or impedance matching. The hermetically sealed structures described above in illustrations of the present invention are thus simple in construction and inexpensive to manufacture. In the case in which an antenna coupled to the elliptical waveguide employs two-frequency cross polarization, it is possible to simplify greatly the hermetically sealed structure for the junction between an elliptical waveguide and a circular waveguide by employing the embodiment shown in Figs. 4(a) and 4(b). Although certain preferred embodiments of the present invention have been shown and described in detail, by way of example, it should be understood that various changes and modifications thereof, as well as other embodiments, may be made without departing from the scope of the protection sought by the appended claims.

Claims: A hermetically sealed structure for a junction between two circular waveguides (1,2), in which a hermetic seal (3) is sandwiched between the respective ends of the two circular waveguides, which structure includes a first circular waveguide having an inside diameter which is gradually reduced continuously towards an end thereof, which end is to be joined to an end of a second circular waveguide; and a second circular waveguide (2) having an end to be joined to the end of the first circular waveguide (1); the first circular waveguide (1) and the second circular waveguide (2) having different inside diameters at the ends which are to be joined via the hermetic seal (3). A hermetically sealed structure as claimed in claim 1, wherein one of the first and second circular waveguides (1,2) is an antenna waveguide for connection to an antenna device, and the other of the first and second circular waveguides (1, 2) is a feeder waveguide for connection to a radio transmitter/receiver device. A hermetically sealed structure for a junction between an elliptical waveguide (1) and a circular waveguide (2), in which a hermetic seal (3) is sandwiched between the respective ends of the elliptical waveguide (1) and the circular waveguide (2) which structure includes an elliptical waveguide (1) having an inside dimension which is gradually reduced continuously, the similarity of its shape being kept, towards an end thereof, which end is to be joined to an end of a circular waveguide (2); and a circular waveguide (2) having an end to be joined to the end of the elliptical waveguide (1); the elliptical waveguide and the circular waveguide having different inside dimensions at the ends which are to be joined via the hermetic seal (3). A hermetically sealed structure as claimed in claim 3, wherein the elliptical waveguide (1) is an antenna waveguide for connection to an antenna device, and the circular waveguide (2) is a feeder waveguide for connection to a radio transmitter/receiver device.

Inventors: UMEZU KEIICHI, UMEZU, KEIICHI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1996
Main classification: H01P1
IPC codes: H01P1