MICROWAVE ANTENNAS

Abstract: A microwave antenna (10) is formed from a stack of generally planar elements (14-22) forming an array of horns (12) communicating with waveguides (38). The generally planar elements (14-22) are of metallised plastics. Each of these elements (14-22) has a given overall thickness which is constituted by a membrane of relatively small thickness formed (typically by vacuum forming) into a corrugated shape.

Description: "Microwave Antennas" This invention relates to antennas, particularly (but not exclusively) planar antennas for receiving microwave signals such as direct broadcasting by satellite (DBS) signals. There are known planar antennas comprising an array of horns communicating with one or more waveguide systems, and in which the horns and waveguides are formed from a sandwich of moulded planar members. The planar members may be plastics mouldings with electrically conductive surfaces formed by metallisation. See for example my published International Patent Applications WO89/09501 and WO91/20109. While antennas of the foregoing type have proved successful, there is a need for further improvement with a view to ease of mass manufacture and reduction in manufacturing cost. Accordingly, the present invention provides an antenna comprising a plurality of generally planar members secured together in face-to-face relationship to form an array of cavities and a waveguide system, each cavity being in communication with at least one waveguide channel, each of the planar members having a given overall thickness transverse to its principal plane, said thickness being constituted by a membrane of relatively small thickness formed three- dimensionally in a generally corrugated fashion. Preferably, each of the planar members is a vacuum forming. Preferably, each of the planar members is formed by vacuum forming a plastics material and thereafter metallising at least one side of the vacuum formed material. From another aspect, the present invention provides a method of manufacturing an antenna, comprising forming a plurality of generally planar members, each of the planar members having a given overall thickness transverse to its principal plane, said thickness being constituted by a membrane of relatively small thickness formed three-dimensionally in a generally corrugated fashion, positioning the planar members in face-to-face relationship to form an array of cavities and a waveguide system, each cavity being in communication with at least one waveguide channel, and securing the planar members together. In a preferred form of the invention, the planar members are secured together by ultrasonic welding; for this purpose the mating faces of the planar members may be provided with ribs or the like which fuse to form weld beads during the ultrasonic welding. Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which: Fig. 1 is an isometric view, sectioned along a transverse plane, of an antenna element according to the present invention; Fig. 2 shows part of Fig. 1 in greater detail, to an enlarged scale; Fig. 3 illustrates a preferred means used in securing together parts of the assembly of Figs. and 2; Fig. 4 is a plan view illustrating the construction of a modified form of waveguide channel; and Fig. 5 is an enlarged cross-sectional scrap view on the line 5-5 of Fig. 4. Referring particularly to Figs. 1 and 2, an antenna element generally designated at 10 is in the form of a 4x4 array of receiving horns 12. In practice, the element 10 would be assembled with like elements to provide a larger array as a single antenna. The antenna element 10 comprises five generally planar members 14 - 22. The first planar member 14 is formed to provide the horns 12, each of which is of tapering square section, terminating in a lower wall 24 and circular aperture 26. The second and third planar members 16, 18 together define cylindrical cavities 28 aligned with the circular apertures 26, and first closed, rectangular section channels 30 extending along the length of the antenna element 10. The cavities 28 terminate in a plane partial end wall 32 defining a D-shaped slot 34. The fourth and fifth planar members 20, 22 together define bottom sections 36 to the horn cavities, and second closed, rectangular section passages 38. Each bottom section 36 has an upper part 39 corresponding to the D-shaped slots 34, and a lower part 40 forming an open-topped channel communicating with one of the second passages 38. The first channels 30 communicate with the cavities 26 by means of passageways 40 as indicated in Fig. 2. Each of the planar members 14 - 22 is separately formed by vacuum forming of a suitable plastics material. Techniques of and materials for vacuum forming are well known per se and will not therefore be described in detail herein. The walls of the horns, cavities and channels have the effect of providing a corrugated formation to each member, thus giving a reasonable degree of rigidity which is increased when the five members are secured together. After vacuum forming, one side, as appropriate, of each member is metallised in any suitable fashion, and thus when the members are secured together the surfaces of the horns, cavities and channels which are adjacent the received microwave radiation are conductive metallised surfaces. The channels 30 and 38 thus act as waveguides for differently polarised microwave signals separated by the conformation of the cavities 26, as is known per se. The five members may be secured together in any suitable manner. For example, they may be secured together by adhesive. A preferred feature of the present invention, however, is to secure the planar members together by means of ultrasonic welding. For this purpose, as illustrated in Fig. 3, the mating faces such as the lower face 50 of the first member 14 and the upper face 52 of the second member 16, are provided with ribs 54 which fuse to form continuous welded beads during ultrasonic welding. Referring to Figs. 4 and 5, there is illustrated an alternative construction of a moulded element 60 which partially defines the wave guides, for example in substitution for the element 22 in the above embodiment. Fig. 4 shows a 12 x 12 array, but it will be understood that the arrangement can be applied to any desired size of array. The element 60 is once again a vacuum forming in which a single membrane of material is formed to provide upper faces 62 and lower faces 64 joined by side webs 65 to define waveguide channels 66. In this embodiment, however, the upper faces 62 are defined only as flanges in the vicinity of the waveguide channels 66, and elsewhere the material is cut away to form void spaces 68. This configuration is particularly efficient and results in a weight reduction of approximately 30%. In addition, the particular design minimises the extent of area which requires to be metallised.

Claims: CLAIMS 1. An antenna comprising a plurality of generally planar members secured together in face-to-face relationship to form an array of cavities and a waveguide system, each cavity being in communication with at least one waveguide channel, each of the planar members having a given overall thickness transverse to its principal plane, said thickness being constituted by a membrane of relatively small thickness formed three- dimensionally in a generally corrugated fashion. 2. An antenna according to claim 1, in which each of the planar members is a vacuum forming. 3. An antenna according to claim 2, in which each of the planar members is formed by vacuum forming a plastics material and thereafter metallising at least one side of the vacuum formed material. 4. An antenna according to any preceding claim, in which each of said membranes is continuous across the whole area of the antenna. 5. An antenna according to any of claims 1 to 3, in which the waveguide channel is partially defined by one said membrane which is cut away to form void spaces in areas of the membrane not immediately adjacent the waveguide channel. 6. A method of manufacturing an antenna, comprising forming a plurality of generally planar members, each of the planar members having a given overall thickness transverse to its principal plane, said thickness being constituted by a membrane of relatively small thickness formed three- dimensionally in a generally corrugated fashion, positioning the planar members in face-to-face relationship to form an array of cavities and a waveguide system, each cavity being in communication with at least one waveguide channel, and securing the planar members together. 5. A method according to claim 4, in which the planar members are secured together by ultrasonic welding. 6. A method according to claim 5, in which the mating faces of the planar members are provided with ribs or the like which fuse to form weld beads during the ultrasonic welding.

Inventors: COLLINS JOHN LOUIS FREDERICK C, COLLINS, JOHN, LOUIS, FREDERICK, CHARLES
Applicants: COLLINS JOHN LOUIS FREDERICK C, FORTEL TECHNOLOGY LTD, COLLINS, JOHN, LOUIS, FREDERICK, CHARLES, FORTEL TECHNOLOGY LIMITED
Application year: 1995
Main classification: H01Q21
IPC codes: H01Q13, H01Q21