Microwave antennas

A microwave antenna (10) is formed from a stack of generally planar elements (14-122) forming an array of horns (12) communicating with waveguides (38). The generally planar elements (14-22) are of metallized 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.

This invention relates to antennas for receiving microwave signals.
 There are known antennas comprising an planar 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, WO91/20109 and WO95/23440.
 There remains an on-going need for improvement to ease manufacture and
 reduce manufacturing time and cost. It is also necessary to address the
 design of other than planar arrays.
 Accordingly, the present invention provides an antenna comprising :
 a plurality of planar members secured together in face-to-face relationship
 to form an array of cavities, each cavity being in communication with at
 least one waveguide channel;
 a waveguide system and;
 a single waveguide output port.
 Preferably, said single output port is circular.
 Preferably, said single output port is connectable to a low noise block
 converter.
 Preferably, each of the members is a vacuum forming.
 Preferably, the members are 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 element comprising an array of receiving horns,
 cylindrical cavities aligned with the receiving horns and bottom sections
 for the cavities, wherein the array of receiving horns is formed from a
 first planar member, the cylindrical cavities are formed from a second
 planar member in conjunction with a third planar member, and the bottom
 sections are formed from the third planar member in connection with a
 fourth planar member, 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.

Referring particularly to FIGS. 1 to 4, an antenna element generally
 designated 10 in in the form of a 4.times.4 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 four generally planar members 14-20.
 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 planar member 16 together with the upper portion of the third
 planar member 18 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 29 terminate in a
 plane partial end wall 32 defining a D-shaped slot 34.
 The lower portion of the third planar member 18 together with the fourth
 planar member 20 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 lover 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 14-20 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.
 FIGS. 3 and 4 show the construction of the third planar member 18,
 previously formed from separate members, formed as a single mould.
 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 four 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 with 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 four 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. 5 to 8, there is illustrated an alternative construction
 of a moulded element 60 which partially defines the wave guides, for
 example in substitution for the element 20 in the above embodiment.
 FIG. 4 shows a 12.times.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. The singular circular output port 70 provides an interface for
 a low noise block converter interface.
 It is envisaged that this antenna will also be of use in communication and
 automotive purposes.
 The reduction in the number of separate mouldings results in a 25%
 reduction in assembly steps.