CA2184080A1 - Microwave antennas - Google Patents

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

21 ~4080 21 " Mi ~- rowave ~ntF-nn;- ~ -3 This invention relates to antenna6, partic~ r]y (but 4 not exclusively) planar antennas for receiving 5 microwave signal6 such as direct broadcasting by 6 satellite (DBS) signals.

8 There are known planar antennas comprising an array of 9 horns ~ ating with one or more waveguide systems, 10 and in which the horns and waveguides are formed from a 11 sandwich of moulded planar members. The planar members 12 may be plastics mouldings with electrically conductive 13 surfaces formed by metallisation. See for example my 14 published International Patent Applications WOB9/09501 and WO91/20109.

17 While antennas of the foregoing type have proved 18 successful, there ig a need for further i uv, L
19 with a view to ease of mass manufacture and reduction 20 in manufacturing cost.

22 Accordingly, the present invention provides an antenna 23 comprising a plurality of generally planar members 24 secured together in face-to-face relationship to form Wogs/23440 ~ 1 840~0 an array of cavities and a waveguide 6ystem, each 2 cavity being in _ i ~ation with at least one 3 w~veguide channel, each of the planar members having a 4 given overall thirknaRs transverse to its principal 5 plane, said thirknr~ss being constituted by a membrane 6 of relatively small thirknr~sS formed three-dimensionally in a generally co.Luy~ted fashion.

9 Preferably, each of the planar members is a vacuum 10 f orming .

12 Preferably, each of the planar members is formed by 13 vacuum forming a plastics material and thereafter 14 met~71iRin~ at least one side of the vacuum formed 15 material.

17 From another ~spect, the present invention provides a 18 method of manufacturing an antenna, comprising forming 19 a plurality of rJ~-nr~rAl ly planar members, each of the 20 planar members having a given overall thirkn"ss 21 transverse to its principal plane, said thirknr~ss being 22 constituted by a ` ~n~ of relatively 5mall th i rknr~c8 23 formed three-dimensionally in a generally corrugated 24 fashion, positioning the planar members in face-to-face 25 relatinn~hi~ to form an array of cavities and a 26 waveguide system, each cavity being in ~ i ration 27 with at least one waveguide channel, and securing the 2 8 planar members together .

30 In a preferred form of the invention, the planar 31 members are secured together by ultrasonic welding; for 32 this purpose the mating faces of the planar members may 33 be provided with ribs or the like which fuse to form 34 weld beads during the ultrasonic welding.

~ 2~ 840~0 Wo sst23440 3 ~ E
Embodiment6 of the present invention will now be 2 described, by way of example only, with reference to 3 the drawings, in which:

Fig. 1 i6 an isometric view, sectioned along a 6 Llhh~vt:Lr.e plane, of an antenna element according 7 to the present invention;

8 Fig. 2 shows part of Fig. 1 in greater detail, to 9 an enlarged scale;
Fig. 3 illustrates a preferred means used in 11 securing together parts of the assembly of Figs. 1 12 and 2;
13 Fig. 4 is a plan view illustrating the 14 co.~sLLu~;Lion of a modified form of waveguide channel; and 16 Fig. 5 is an enlarged cross-sectional scrap view 17 on the line S-S of Fig. 4.

19 Referring particularly to Figs. 1 and 2, an antenna element generally designated at 10 is in the form of a 21 4x4 array of receiving horns 12. In practice, the 22 element 10 would be assembled with like elements to 23 provide a larger array as a single antenna. The 24 antenna element 10 comprises five generally planar members 14 - 22.

27 The first planar member 14 is formed to provide the 28 horns 12, each of which is of tAr~rin~ square section, 29 terminating in a lower wall 24 and circular tlpt~L Lul~:
26.

32 The second and third planar members 16, 18 together 33 define cylindrical cavities 28 aligned with the 34 circular apertures 26, and first closed, rectangular section channels 30 extending along the length of the , 21 ~80 Wo 9SI23440 P_ 1 .

antenna element 10. The cavities 28 terminate in a 2 plane partial end wall 32 defining a D-shaped slot 34.
4 The fourth and fifth planar members 20, 22 together 5 define bottom sections 36 to the horn cavities, and 6 second closed, rectangular section passages 38. Each 7 bottom section 36 has an upper part 39 ~,:VL r t,~vllding to 8 the D-shaped slots 34, and a lower part 40 forming an 9 open-topped channel ,_ n i cating with one of the second passages 38.

12 The first ~hAnnP1R 30 c, icate with the cavities 26 13 by means of pas~as_yD 40 as indicated in Fig. 2.

15 Each of the planar members 14 - 22 is separately formed 16 by vacuum forming of a suitable plastics material.
17 T~rhniq~ of and materials for vacuum forming are well 18 known ~ and will not therefore be described in 19 detail herein. The walls of the horns, cavities and 20 ~hAnn~ have the effect of providing a corrugated 21 formation to each member, thus giving a reasonable 22 degree of rigidity which is increased when the five 23 members are secured together.

25 After vacuum forming, one side, as appropriate, of each 26 member is metallised in any suitable fashion, and thus 27 when the members are secured together the surfaces of 28 the horns, cavities and ~hAnn~ which are adjacent the 29 received microwave radiation are conductive metallised 30 surfaces . The ~ hAnn~ 30 and 38 thus act as 31 waveguides for differently polarised microwave signals 32 separated by the conformation of the cavities 26, as is 3 3 known ~ .

35 The f ive members may be secured together in any 2~ ~0~
wo gsl23440 r~
s suitable manner. For example, they may be secured 2 together by adhesive. A preferred feature of the 3 present invention, however, i8 to 6ecure the planar 4 members together by mean6 of ultr;l~sn;r- welding. For 5 this purpose, as illustrated in Fig. 3, the mating 6 faces such as the lower face S0 of the first member 14 7 and the upper face 52 of the second member 16, are B provided with ribs 54 which fuse to form cont 9 welded beads during ultrasonic welding.
11 Referring to Figs. 4 and 5, there is Lllustrated an 12 alternative cul".-Lu~;Lion of a moulded element 60 which 13 partially defines the wave guides, for example in 14 substitution for the element 22 in the above : ~i . =

17 Fig. 4 shows a 12 x 12 array, but it will be understood 18 that the ~rrAn, L can be applied to any desired size 19 of array.
21 The element 60 is once again a vacuum forming in which 22 a single membrane of material is formed to provide 23 upper faces 62 and lower faces 64 joined by side webs 24 65 to define waveguide r~h~nn~l f; 66 . In this 25 embodiment, however, the upper faces 62 are defined 26 only as flanges in the vicinity of the waveguide 27 rhAnn~ 66, and elsewhere the material is cut away to 28 form void spaces 68.

30 This configuration is partic~ rly efficient and 31 results in a weight reduction of approximately 309~. In 32 addition, the particular design minimises the extent of 33 area which requires to be metallised.

Claims (6)

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.