GB1559756A

GB1559756A - Microwave antenna and a method of operating it

Info

Publication number: GB1559756A
Application number: GB4122677A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1976-10-06
Filing date: 1977-10-04
Publication date: 1980-01-23
Also published as: FR2367356A1; DE2644980A1; IT1087725B; FR2367356B3; JPS5346252A

Description

(54) A MICROWAVE ANTENNA AND A METHOD OF OPERATING IT (71) We, LICENTIA PATENT VER WALTUNGS G.M.B.H. of 1 Theodor Stern-kai, 6 Frankfurt/Main 70, Federal Republic of Germany, a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a microwave antenna and a method of operating it. Such an antenna has a reflector dish. These antennae are used in fixed and movable directional radio paths and when setting up satellite ground stations.

The curve of such a reflector may only deviate to a very small extent from the predetermined desired value so that the required electrical values of the antenna may be maintained. This is also true with respect to the very different temperature relationships in which this type of antenna is operated. If the surface of the reflector becomes coated with ice for example the changes in the electrical propertis are no longer negligible and this has led to this type of antenna usually being provided with a heating device in order to prevent the disruptive formation of ice. In fact it has been proved that with these antennae undesirable and non-negligible deviations from the pedetermined curve of the reflector arise caused by temperature factors.

The present invention therefore seeks to avoid or reduce these distortions of the reflector in the simplest possible manner.

According to one aspect of the invention.

there is provided a method of operating a microwave antenna having a reflector dish comprising operating the reflector dish such that it has as small as possible a temperature gradient over its volume during operation of the antenna, the reflector dish being heated from the rear and having its rear side enclosed by a heat insulating layer.

According to a second aspect of the invention, there is provided a microwave antenna comprising a reflector dish having means for heating its rear surface and a heat insulating layer enclosing rear surface.

The heating of the reflector dish if carried out accurately enables a temperature gradient to be avoided together with its disruptive results.

The provision of a heat insulating layer prevents disruptive distortion from taking place. This is advisable because the antennae having a substantially different ambient temperature on the rear side of the reflector as compared to the front side of the reflector as compared to the front side of the reflector.

Large antennae reflectors are constructed usually in box shape for reasons of design in order to avoid bending of the reflecting surface caused by weight and/or pressure of the wind. In a preferred embodiment of the invention the surface of the dish reflecting the rays may be heated on its rear side in order to prevent icing over of the antenna and also the other side of the box shaped part is provided, at least partially, with a heat insulating layer. The stated heating device prevents icing over of the reflector dish but at the same time brings about a relatively large temperature gradient in the reflector and this leads to undesirable distortion of the reflecting surface and thus impairs the electrical properties of the antenna. The invention is based on the knowledge that this temperature gradient must be prevented in order to avoid damaging distortion. This can only be carried out with very great difficulty and above all can only be carried out subsequently with great difficulty in already existing antennae. Thus the invention solves this object in the stated antenna in that the other side of the box shaped reflector is provided also at least partially with a heat insulating layer. The reflector dish which is heated from its rear side radiates the heat over its surface again.

Since the configuration of the reflector dish iis not usually a simple metal plate, for mechanical reasons, but a complicated carrier construction, the irradiation heat or transmission of heat to other parts connected to the reflector dish takes place in various different ways. In addition there are the changing surrounding temperatures during operation of the antenna so that with these antennae a relatively large temperature gradient may occur within its volume.

These temperature differences must therefore be avoided or kept as small as possible.

With the present design of the usually box shaped construction of the reflector dish, this may be achieved, for example by coating the box shaped part externally with a heat insulating layer. In addition this part may be at least partially heat insulated on the inside, for example by foam.

Normally the reflector dishes of microwave antennae are constructed from metal.

The solution in accordance with the invention of the present object is however not limited to metal reflectors. It may also be used, in a suitable modification, in a reflector dish which is formed by a metal coated plastics construction, i.e. in antennae which are used among other things in communications satellites.

With very large reflector dishes the reflector must be put together from several individual parts for reasons of design. Thus the large reflectors of a satellite ground station are divided up for example into several rings which are subdivided in turn into individual portions. Known microwave antennae of this type have three annular subdivisions for example with a total of 64 individual parts these being joined together in construction of the antenna to form the desired reflector dish. Thus each individual element must be adjustable so that the prescribed curve of the whole reflector is provided as accurately as possible. It is just with these very large microwave reflectors that the distortions described at the outset are particularly disadvantageous, since they attain an order of magnitude which is extremely disruptive in relation to the operating wavelength.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 is a diagram showing the distortion in an antenna, and Figure 2 is a view of an antennae part constructed in accordance with the invention.

In Figure 1 for the last above mentioned antenna a curve is plotted over the length L of a reflector part, the distortion was measured in a practical case. As a result of nonuniform heating of this dish shaped reflector part its upper side reflecting the microwave radiation was bent forward in accordance with the curve shown in Figure 1. Bending of 0.1 - 0.2 mm. per "C was measured which with temperature gradients arising in practice may lead to values which are impermissible in comparison to the operating wavelength.

Figure 2 shows a part (panel) constructed in accordance with the present invention for a reflector dish. The metal plate is designated 1 and reflects the microwave radiation on its one surface 2. The plate 1 is added to form a box shaped part by means of metal parts 3, 4, 5 and 6 constructed in U shape in the embodiment shown. On the rear side 7 of the plate 1 a heating device 8 is arranged preventing icing over of the reflector dish.

In order to make sure that no impermissible temperature gradient arises between the limbs of the U shaped parts 4, 5, 6 connected to the plate 1 and the opposite limbs 10, 12, 13, 14, the outer side of the box shaped reflector part must be insulated in terms of heat. In the embodiment shown, a layer 11 comprising a suitable dielectric was used for this purpose surrounding the box shaped part on its rear side and insulating it in terms of heat from the surroundings.

Since the plate 1 emits energy the rear side limbs 10, 12, 13 and 14 may in some circumstances accept a fairly large temperature for example as a result of localisation of heat and this would also mean distortion but in the other direction. This may be avoided by means of suitable additional insulation which either partially or completely fills up the chamber 9.

Another possibility lies in insulating the heated reflector surface 1 by means of heat technology from the rear side stiffening construction so that it may accept the surrounding temperature over its entire volume.

In each case, application of the heat insulating dielectric must be undertaken so that as far as possible there is no temperature gradient occurring in the volume of the reflector dish while taking into account the conditions of use of the whole antennae (heating, ambient temperature, design). In the embodiment shown, care must be taken as required by the present construction that the same temperature prevails on both sides of the stiffening construction so that this and together with it, plate 1, are not distorted.

The undesirable distortion of the reflector dish shown in Figure 1 could be reduced, even in the first tests by 1/10 of the original value by using the theory given in the invention and distortion could be achieved which is negligible in practice in relation to the operating wavelength.

WHAT WE CLAIM IS:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. reflector dish which is heated from its rear side radiates the heat over its surface again. Since the configuration of the reflector dish iis not usually a simple metal plate, for mechanical reasons, but a complicated carrier construction, the irradiation heat or transmission of heat to other parts connected to the reflector dish takes place in various different ways. In addition there are the changing surrounding temperatures during operation of the antenna so that with these antennae a relatively large temperature gradient may occur within its volume. These temperature differences must therefore be avoided or kept as small as possible. With the present design of the usually box shaped construction of the reflector dish, this may be achieved, for example by coating the box shaped part externally with a heat insulating layer. In addition this part may be at least partially heat insulated on the inside, for example by foam. Normally the reflector dishes of microwave antennae are constructed from metal. The solution in accordance with the invention of the present object is however not limited to metal reflectors. It may also be used, in a suitable modification, in a reflector dish which is formed by a metal coated plastics construction, i.e. in antennae which are used among other things in communications satellites. With very large reflector dishes the reflector must be put together from several individual parts for reasons of design. Thus the large reflectors of a satellite ground station are divided up for example into several rings which are subdivided in turn into individual portions. Known microwave antennae of this type have three annular subdivisions for example with a total of 64 individual parts these being joined together in construction of the antenna to form the desired reflector dish. Thus each individual element must be adjustable so that the prescribed curve of the whole reflector is provided as accurately as possible. It is just with these very large microwave reflectors that the distortions described at the outset are particularly disadvantageous, since they attain an order of magnitude which is extremely disruptive in relation to the operating wavelength. The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 is a diagram showing the distortion in an antenna, and Figure 2 is a view of an antennae part constructed in accordance with the invention. In Figure 1 for the last above mentioned antenna a curve is plotted over the length L of a reflector part, the distortion was measured in a practical case. As a result of nonuniform heating of this dish shaped reflector part its upper side reflecting the microwave radiation was bent forward in accordance with the curve shown in Figure 1. Bending of 0.1 - 0.2 mm. per "C was measured which with temperature gradients arising in practice may lead to values which are impermissible in comparison to the operating wavelength. Figure 2 shows a part (panel) constructed in accordance with the present invention for a reflector dish. The metal plate is designated 1 and reflects the microwave radiation on its one surface 2. The plate 1 is added to form a box shaped part by means of metal parts 3, 4, 5 and 6 constructed in U shape in the embodiment shown. On the rear side 7 of the plate 1 a heating device 8 is arranged preventing icing over of the reflector dish. In order to make sure that no impermissible temperature gradient arises between the limbs of the U shaped parts 4, 5, 6 connected to the plate 1 and the opposite limbs 10, 12, 13, 14, the outer side of the box shaped reflector part must be insulated in terms of heat. In the embodiment shown, a layer 11 comprising a suitable dielectric was used for this purpose surrounding the box shaped part on its rear side and insulating it in terms of heat from the surroundings. Since the plate 1 emits energy the rear side limbs 10, 12, 13 and 14 may in some circumstances accept a fairly large temperature for example as a result of localisation of heat and this would also mean distortion but in the other direction. This may be avoided by means of suitable additional insulation which either partially or completely fills up the chamber 9. Another possibility lies in insulating the heated reflector surface 1 by means of heat technology from the rear side stiffening construction so that it may accept the surrounding temperature over its entire volume. In each case, application of the heat insulating dielectric must be undertaken so that as far as possible there is no temperature gradient occurring in the volume of the reflector dish while taking into account the conditions of use of the whole antennae (heating, ambient temperature, design). In the embodiment shown, care must be taken as required by the present construction that the same temperature prevails on both sides of the stiffening construction so that this and together with it, plate 1, are not distorted. The undesirable distortion of the reflector dish shown in Figure 1 could be reduced, even in the first tests by 1/10 of the original value by using the theory given in the invention and distortion could be achieved which is negligible in practice in relation to the operating wavelength. WHAT WE CLAIM IS:

1. A method of operating a microwave antenna having a reflector dish comprising operating the reflector dish such that it has as small as possible a temperature gradient over its volume during operation of the antenna, the reflector dish being heated from the rear and having its rear side enclosed by heat insulating layer.

2. A microwave antenna comprising a reflector dish having means for heating its rear surface and a heat insulating layer enclosing its rear surface.

3. An antenna for carrying out the method according to claim 2, wherein the reflector dish is box shaped.

4. An antenna according to claim 3, wherein the rear side of the reflector is heat insulated with respect to the box shaped carrier construction of the dish.

5. An antenna according to claim 3, 4, 5 wherein the side of the dish reflecting the rays is heated on its rear side and that also the other side of the box shaped part is provided at least partially with a heat insulating layer.

6. An antenna according to claim 5.

wherein the box shaped part is foamed on the inside with a dielectric.

7. An antenna according to claim 5, or 6, wherein the box shaped part is coated on the outside with a heat insulating layer.

8. An antenna according to any one of claims 4 to 7 wherein the box shaped reflector dish is constructed completely from metal.

9. An antenna according to claim 4 or 5, wherein the reflector dish is formed from a metal coated plastics construction.

10. An antenna according to any one of claims 2 to 9, wherein the reflector dish is assembled from several preferably adjustable individual elements.

11. A method of driving microwave antennae according to claim 1 and substantially as described herein.

12. A microwave antenna substantially as described herein with reference to the drawings.