GB2250135A

GB2250135A - Antenna feed arrangements

Info

Publication number: GB2250135A
Application number: GB9023542A
Authority: GB
Inventors: James Owen Mccormack
Original assignee: GLASNOST INTERNATIONAL PLC; SHERATON INVESTMENTS Ltd
Current assignee: GLASNOST INTERNATIONAL PLC; SHERATON INVESTMENTS Ltd
Priority date: 1990-10-30
Filing date: 1990-10-30
Publication date: 1992-05-27
Anticipated expiration: 2010-10-30
Also published as: GB9023542D0; GB2250135B

Abstract

A feed horn 4 for a satellite dish 1 is movable by means of an actuator 5 which may be electrically, mechanically or hydraulically driven. The orientation of the feed horn may thus be varied so that reflected signals from a plurality of satellites may be received. A guide limb (102), fig 5 may be connected to the feed horn and mounted in a slot (101), in a relatively stationary guide plate (100), so that the feed horn may swing in an arcuate manner and point to the correct region of the so-called "Clark Belt" in the sky. <IMAGE>

Description

Automatic Feed Horn This invention relates to automatic feed horns which are specifically, but not exclusively, intended for use with satellite antennas.

A problem in the past has been that satellite antennas must be pointed to a particular region in the sky from where a satellite signal emanates. Sometimes when it is desired to alter the direction of the satellite antenna, so that it points in a different direction in order that it may receive a different signal from another satellite, it has been necessary to move the satellite antenna with actuators. A problem with these actuators has been that they are large and cumbersome. They are also expensive to install and maintain and because they are heavy they have required substantial bracketing to fix them to walls or roofs.

According to the present invention there is provided an actuator arranged to move a feed horn relative to the surface of an antenna.

Preferably the feed horn is positioned at the focus of the antenna and the actuator is;proximal to the feed horn so that the orientation of the feed horn may be varied in such a manner that reflected signals from a plurality of satellites may be received.

Advantageously a plate, which may be formed from metal, has a slot cut in it. This slot acts as a guiding groove for a guide limb of the actuator. The actuator therefore drives the feed horn in such a way that it follows an arcuate path. The arcuate path is such that the feed horn traverses the "belt" in which satellites, are found. This belt is known as the "Clark Belt".

The slot may have a coating, such as PTFE, to reduce friction between the surface of the slot and the guide limbs.

Because the feed horn is much lighter than a large antenna dish it has substantially less inertia and requires only a small motor or hydraulic actuator to move it relative to the surface of the antenna. Also, because the antenna does not have to move, it may be permanently attached by way of rigid brackets or scaffolding to a wall or roof.

Another problem has been that because the surface of the antenna is relatively large it presented a large cross section to wind and therefore had a large wind resistance and as a result of this substantial motors and/or actuators have been required to move it in the past.

The actuator to drive the feed horn may be supported on three or more rigid members extending from the rim or from points on the surface of the antenna.

The power supply for the motor may be supplied by way of a small cable passing along one of these support stilts or it may be a replaceable battery which may be inserted into the actuator of the feed horn.

The actuator may operate by way of a rack and pinion device. Preferably a motor is fitted with a small gear which may engage with a rack, and because the movements of the feed horn are relatively small compared with movements of an overall dish, the feed horn need only swing through a relatively small angle.

Of course variation may be made and the feed horn may be remote from the antenna. For example it may be mounted on a small rail and be movabale backwards and forwards on this rail in an arcuate manner.

Alternatively movement may be provided by way of an hydraulic actuator which may constitute a cylinder and piston ram arrangement.

An embodiment of the present invention will now be described by way of examples only and with reference to the accompanying figures in which: Fig. 1 illustrates a diagramatical view of an antenna having a feed horn; Fig. 2 illustrates an example of an actuator having a sun and planetary gear drive system for the feed horn; Fig. 2a illustrates a sectional view of fig. 2 and.

shows the sun and planetary gear system in detail; Fig. 3 illustrates an alternative embodiment of a drive system having an hydraulic actuator; Fig. 4 illustrates an alternative embodiment of a drive system having a rack and pinion actuator; and Fig. 5 illustrates diagramatically the relationship between an actuator, a feed horn and a guide plate.

Fig 1 shows an antenna 1 which is dish shaped and is mounted by way of support struts 2 onto a wall of a house 3. A feed horn 4 is mounted on an actuator 5, which is itself at the focus of the antenna dish 1.

The actuator 5 points the feed horn 4 at the surface of the dish 1. The actuator 5 is a small electric motor within a sun and planetary gear system, as shown in detail in fig. 2a. The feed horn 4 is swung backwards and forwards from the two extremes of the double headed arrow A-B to the position shown in ghost lines of the feed horn 4' and the actuator 5'.

An electrical conductor 12 passes along the support strut 13a. Clearly it is desirable to have the effective cross sectional area of the feed horn and actuator 5 as small as possible as this acts as an impeding body to incident microwaves. The electrical conductor 12 is attached by way of grips 14 to the back of the dish. A coaxial cable or microwave guide 20 passes from the reception end of the feed horn 4, and is guided down another stilt 13b of the antenna and into the house where it is demodulated and decoded by suitable equipment.

Referring to fig. 2, which shows an overall view of the motorised feed horn and shows diagramatically the sun and planetary drive mechanism. The electric motor 21 is housed within the actuator housing 5. The electric motor 21 is connected by way of a drive shaft 22 to a planetary gear cog 23. This is maintained within an orbital relationship to a sun gear cog 24, by way of a peripheral gear train 25. The sun and planetary gear arrangement is shown in detail in fig.

2a. The power supply to the motor 21 is by way of a cable 12 which is supported by, or in, one of the support struts 13. The microwave feed horn 4 is shown in ghost lines. The detector 40 which is at the end of the microwave feed horn and is connected to a co-axial cable 14 which passes to the decoder 50 in the house.

Fig. 2a shows a sectional view of the arrangement of fig. 2 and shows in detail the sun gear 24 and the planetary gear cog 23, which moves around the sun cog 24 and is supported by the peripheral gear train 25. The feed horn 4 is connected to the gear drive mechanism in such a way that it swings in the arcuate manner as depiçted by the double headed arrow A-B.

Fig. 3 shows another alternative embodiment of the feed horn. The feed horn 4 is connected to an hydraulic actuator 50. A ram 51 drives the feed horn backwards and forwards so that it is swung in a direction of the arcuate arrow A-B. An hydraulic source is provided at 52 and this may be mounted behind the antenna. Suitable valves 53 and 54 are provided on the fluid lines so that the piston 55, shown in ghost lines within the hydraluic actuator 50, moves backwards and forwards in the direction of double headed arrow C-D. The embodiment of fig. 3 otherwise functions in exactly the same way as that shown in figs. 2 and 2a. The co-axial cable 14 passesfrom the back of the feed horn to processor and demodulator 50.

Fig. 4 shows an alternative embodiment where like parts bear the same reference numerals. The feed horn 4 is mounted on a fixed pivot 99 by way of rack 60 and pinion 61. The feed horn 4 therefore swings as mentioned above in an arcuate fashion. The rack 60 is curved so that the gear 61 may "run" along it and the feed horn may swing to-and-fro accordingly. The distance between the pivot point 99 and the centre of the gear 61 may be varied so as to increase the leverage available to drive the feed horn.

Fig. 5 shows a guide plate 100 which has a slot 101 cut in it.

A guide limb 102 passes through the slot, such that when actuator 103 moves feed horn 104, the path followed by the feed horn is such that the feed horn points in the direction to receive a signal from a satellite in the Clark Belt. The guide plate 100 therefore acts to move the feed horn up and down by way of the arcuate slot 101.

Guide limb 102 is connected to a pivot 109. This is a ball-in socket joint.

Variation may be made to the invention for example it is possible to arrange two actuators to move the feed horn into a variety of positions which would described the surface of a sphere, instead of the arc of a circle.

This would enable even greater flexibility of the arrangement as the feed horn could then point at any particular region in space instead of, traversing a narrow band such as the Clark Belt.

Similarly a microprocessor may be provided which could store information as to the position of the feed horn, and the direction in which the feed horn should be pointed which corresponds to a particular satellite signal.

Similar variation may be made to the shape of the antenna dish which could become a "banana shaped" slice, as it is only the central portion of the dish which is now actively used. This could reduce costs of production of the dish, as well as its wind resistance.

Claims

1. An actuator arranged to move a feed horn relative to the surface of an antenna.

2. An actuator according to claim 1 wherein the feed horn is positioned substantially at the focus of the antenna.

3. An actuator according to claim 1 or 2 wherein the actuator is located proximal to the feed horn, so that the orientation of the feed horn may be varied in such a manner that reflected signals from a plurality of sources may be received.

4. An actuator according to any preceding claim, located on a support, the support having a plate with having a slot formed in it, so that the slot acts as a guiding groove for a guide limb.

5. An actuator according to claim 4 wherein the slot is an arcuate slot.

6. An actuator according to claim 5 wherein the arcuate slot has a lining to reduce the friction between the surface of the slot and a guide limb.

7. An actuator according to any preceding claim wherein a motor is used to drive the feed horn.

8. An actuator according to any of claims 1 to 6 wherein an hydraulic actuator is used to move the feed horn.

9. An actuator according to claim 7 or 8 wherein end stops are provided to prevent the feed horn moving beyond a predetermined point.

10. An actuator according to any of claim 6 wherein a rack and pinion is arranged to move the feed horn relative to the antenna.

11. An actuator substantially as herein described with reference to the Figures.