NZ208949A - Microwave antenna parabolic reflector - Google Patents

Description

« 2089 4 9 Priority Date(s): .Uf.'.U.TS.? Complete Specification Filed: Class: ..HQj.Q].5/ybv . .^.fl.P5?/.9P.

Publication Date: ... & .9 .^fR JR8.3 ......

P.O. Journal, No: ... GO* i ; PATENT OFFiCE i 19 JUL 1984 Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "MICRO WAVE ANTENNA" -I- WE STIG OLOF ANDERSSON, a Swedish subject of 61 Kvarnaatan, S-335 00 GNOSJO Sweden, and REGIS GUSTAFSSON a Swedish subject of 10 Kopmannagatan, S.335 00 GNOSJO Sweden hereby declare the invention, for which-t/we pray that a patent may be granted to me-Aus, and the method by which it is to be performed, to be particularly described in and by the following statement " (followed by p»j?e 1 A.) 2 089 4q Micro wave antenna This invention relates, to antennas of the kind including a reflecting surface collecting or focusing the radiation. Antennas of this kind are for instance radar antennas, so-called parabolic antennas for transmitting and receiving for instance satellite television as well as antennas for telephone communication. Antennas of this kind have been known for several years and these antennas have been made in different ways. Up to now these antennas have had a tendency to be comparatively expensive to make or of a bad quality due to the fact that the reflecting surface must be very carefully shaped in order to allow an optimum output. Already very small deviations from the ideal surface result in essential power losses. One fabrication method used for the fabrication of antennas of this kind is the enclosing of a metal net in a glassfiber reinforced plastic, which for instance has been shown in the US patent 2 948 896.

Yet another method of fabrication is to coat the reflectory surface of the antenna with a metal, which for instance has been shown in the French patent 2 502 852, which like the device according to the US patent mentioned above is a sandwich-construction, i.e. a construction with several different layers in order to achieve a sufficient strength. These two constructions mentioned are however comparatively expensive to fabricate due to the great number of fabrication steps as well as the amount of used parts . Nor is the desired exactness for the reflectory surface obtained. This exactness in its turn is very important in order to ensure maximum gain for the antenna.

The object of the invention is therefore to define an embodiment and a method for fabrication of parabolic antennas, which is essentially simpler than known technique and at the same time, results in an improved exactness in the reflecting surface.

In accordance with the invention this object is obtained by fabricating the antenna by vaccum or heat shaping a 2 thermoplastic material, that includes a micro wave reflec- ♦ •> ting electrically conductive layer. In this way a reflecting surface with great accuracy is obtained at low cost. The thermoplastic material is suitably in the shape of a sheet on one side of which a metal layer or metal film has been adhered. In accordance with a further development of the invention the metal layer is placed on one side of the thermoplastic layer and in front of the metal layer a further layer of a thermoplastic material is arranged. This further layer in front of the reflecting surface is very thin or has a thickness related to the wave length of the radiation that is to be reflected in order to prevent power losses. This front layer serves to protect the reflective layer and also prevents the antenna from functioning as a sun mirror focusing the sun light on reception means placed in the focus point of the antenna.

Even in this treee layer embodiment of the invention the vaccum or heat shaping of all layers is obtained in one common operation.

According to a further development of the invention the triple layer sheet are achieved by first obtaining a metalic film or a layer on a thermoplastic thin foil, for instance acrylic plastic. In a subsequent operation this foil is adhered to a thicker thermoplastic sheet with the metal side turned against this second thicker and supporting strength providing sheet.

Several different types of material can be used for the fabrication of an antenna in accordance with the invention. For example acrylic can be used and for instance a mixture consisting of 25$ impact resistant acrylic and 75% of a not impact resistant acrylic.

In an antenna particularily adapted to northern latitudes it is possible to arrange heating of the antenna in a known manner behind the shell comprising the above meationedlayers and to arrange a further shel] behind the heatinj? device partly in ,/ 208949 3 order to enclose the heat and partly in order to protect the heating device. These shells enclose a closed intermediate space for the heating device, which space also serves to distribute the heated aiT. In one embodiment of the invention the heating layer, that can consist of resistance wires, heating cloth or the like, and the rear enclosing shell can be shaped in the same operation. Alternatively the method of foaming can be used. By appropriately enclosing.the heating device in this way or another which will be exemplified below it will be possible to feed the heating device directly with a net voltage without an intermediate transformer and without safety risks.

The shaping of the antenna preferably can be made against a positive mould, i.e. that the surface brought in contact with the mould is the front side of the antenna. In this way one also obtains the advantage that the same tool can be used independently of how many layers or how thick the antenna is to be made. In case the heating device is also enclosed in the shaping it is possible, if this consists of radial spokes holding the resistance wires, to obtain radially extending projections in the rear shell or layer, which further increases the stiffness of the antenna. Of course similar reinforcements can be obtained in other ways, for instance by the shaping of a rear shell in a separate operation, a suitable amount of space being provided for the heating device between the front and rear shell of the antenna.

It is of course also possible, in order to place a heating device between the front and rear shell, to include distance elements of a suitable material, e.g. polyurethane. Within the scope of the invention it is of course also possible to carry out the shaping in two steps, so that the front layer or shell is first shaped according to the mould, then the rear shell or layer(s) is heated and shaped -ty- o 208949 by suction or pressure over the first front shell. The invention is below to be described by way of example with reference to the drawings. Fig 1 sho\^s a section through a part of an antenna in accordance with the in-5 vention while figs 2 and 3 show the suspending of the antenna. £7} The antenna shown in fig 1 includes a front shell, which has been given the reference numeral 1. This shell, in its turn has a rear supporting plastic layer 2, a metallic layer 3 10 applied on the front side of this, and about 1 2 j»im (Micrometer) thick and a Drotecting layer in front of the metal layer, the protective layer being 130-150 jxm. and given the re-^ ference number 4. Instead of being built up in this way the front layer can be relatively thin, preferably 1,5 mm 15 at the most, and coated with metal, which on the rear side will be protected in this way in the interior of the antenna. The antenna further includes a rear shell having the reference numeral 5. The front shell 1 and the rear shell 5 are then at the circumference thereof arranged close to 20 each other and sealed with a seal 6 (or by glueing), that runs around the circumference of the antenna. The antenna can either be an unbroken surface or provided with a hole in the middle as is shown. The hole in the middle can be closed in the same way as at the outer edge or in the way 25 shown with a ring 15 between the antenna shells and a rub-v. ber mold 22 gripping this distance ring 15 as well as the two antenna shells.

As can be seen the shells 1 and 5 are so shaped that they define between themselves a space, in which a resistance 30 wire 7 is placed. This is in the left part of the figure shown as secured in a holder 8 extending like spokes and provided with oblique cuts, so that the resistance wire cannot lose its grip. The parts 8 arranged like spokes are fastened to the rear antenna shell, e.g. by rivets 35 23 of plastic. In the right part of fig 1 the resistance 208949 wire 7 is placed on or in an insulating disc 9, which further improves the heating of the front side of the antenna, since the heat from the resistance wire 7 is prevented by the insulation from being led backwards. Since 5 in the right as well as in the left embodiment an air space is present for air circulation behind the front shell of the antenna an even heating of the antenna front shell is ensured.

The antenna is at its outer edge elastically suspended in 10 a circular frame. This elastic fastening is achieved by the aid of rubber elements 10, at which bolts are fastened that in turn are fastened at the antenna and the supporting construction, respectively, which in fig 1 in particular constitutes a frame 11. At the fastening point of 15 the elastic element 10 at the antenna special washers are adapted to the circular shape of the antenna, partly to achieve a good seal and partly to allow as much freedom of movement as possible between the antenna and the supporting frame. Since several elastic fastening elements 20 10 are arranged around the antenna, the antenna always retains the same amount of directional stability as the supporting frame, so that in spite of the elastic arrangement of the antenna, permitting movement due to temperature differences, the antenna always maintains its direc-25 tion, which is very important in order to achieve a good reception.

Fig 2 shows the supporting frame of the antenna shown in fig 1 which is shown here only schematically and given the reference numeral 12. The circular frame 11 is con-30 nected with further details of framework construction that is journalled in an upper journalling point 13 and can be adjusted with a screw 14 to its elevation. The journal 13, as can be seen in particular from fig 3, consists of two ears 17 and 18, a strut 16 arranged be-35 tween these ears and journal not shown therebetween. Since 20894 6 the ears 17 and 18 are relatively far apart a good stability is obtained even if a play should occur in the journal 13. The strut 16 is in its turn fastened to a vertical strut 19, which in turn constitutes a journal for movement in the horisontal plane in a fixed frame, that has been given the reference numeral 20 and which is intended to be fastened to a wall or mast.

At one of the ears 18 is further fastened a latent strut 21 extending to a frame part 20, with which a fine adjustment or change of the direction of the antenna in the horizontal plane can be achieved. By mounting the strut 19 in a way known per se in parallel with the axis of the earth it is possible to use the antenna for receiving or emitting signals from several different satellites. The antenna is changed from one satellite to another only by a small change of the adjustment means 21. The adjustment means 21 can even be replaced by a device driven by an electrical motor.

Finally it should be mentioned that the better precision and the improved design of the antenna in accordance with the invention results in a far stronger signal than what is the case with the known antennas, which in turn means that the antenna in accordance with the invention can be made with approximately 30% smaller diameter than what else should have been possible.

Within the scope of the invention it is also possible to apply the reflective coating after the shaping or forming, e.g. by metal spray. 208949

Claims (6)

WHAT. WE CLAIM IS.;

1. A method of fabricating a bowl shaped reflector for an antenna intended for reception or emission of microwave radiation, which method includes coating a micro-wave 5 reflecting electrically conductive layer of metal onto one side of a thermoplastic foil or film, bonding a thermoplastic sheet ^ of greater thickness than the plastic foil to the metal coating, and vacuum forming or thermoforming the triple layer composite sheet into a bowl shaped reflector. 10

2. A method according to claim 1, characterized in that the vacuum or thermoforming takes place against a mould which is placed on the concave side of the antenna i.e. the reflecting side, and that the thermoplastic layer closest to the mould has the same thickness over its entire area. 15

3. A method according to any one of the preceding claims, characterized in that the triple layer sheet is placed with its thinnest thermoplastic layer against the mould.

4. A method as claimed in claim 1 substantially as herein described with reference to the accompanying drawings. 20

5. An antenna reflector produced by the method of claim 1.

6. An antenna reflector as claimed in claim 5 substantially as herein described with reference to the accompanying drawings. 25 STIG OLOF ANDERSSON and REGIS GUSTAFSSON v v By Their Attorneys BALDWIN, SON & CAREY