GB2225902A

GB2225902A - Dish antenna

Info

Publication number: GB2225902A
Application number: GB8923300A
Authority: GB
Inventors: Sir Clive Marles Sinclair; James St Valentine Westwood
Original assignee: Cambridge Computer Ltd
Current assignee: Cambridge Computer Ltd
Priority date: 1988-10-14
Filing date: 1989-10-16
Publication date: 1990-06-13
Also published as: GB8923300D0

Abstract

The reflector (12) of a dish antenna (1) is a parabolic section of a larger parabola. The section is chosen so that when the antenna is mounted against a vertical wall, the axis of symmetry of the parabola extends at an angle to the horizon substantially equal to the angle of elevation above the horizon of the satellite from which signals are to be received. The antenna is provided with a protective cover (10) which increases the stiffness of the structure and protects the horn (11) and down converter (20) from the weather. An expanded polystyrene filler (25) is interposed between reflector (12) and cover (10) for increased rigidity and horn support. A spherical convex portion (18) on the reverse of reflector (12) is received within a corresponding concave portion (17) of a mounting bracket (14). <IMAGE>

Description

DISH ANTENNA This invention relates to dish antennas, and in particular to dish antennas for receiving satellite television broadcasts.

According to the invention there is provided a dish antenna comprising a ref lector, a horn and a rigid,shaped convex cover, the cover enclosing the horn and being sealed to the periphery of the ref lector.

The provision of a rigid, shaped convex cover sealed to the periphery of the ref lector greatly increases the rigidity of the antenna structure. The effect of this is that the reflector may be made thinner while retaining the exact shape required. A saving in materials results in lower production costs. The convex shape of the cover and its rigidity also contribute to the stiffening of the antenna. Preferably the cover is made out of plastics material. Stiffening may be increased by bonding the cover to the reflector. The cover may be attached to the reflector via a spacer to compensate for the profile of the reflector, which may be square in outline and parabolic in curvature. The cover may be arranged to support the horn at the focus of the reflector.

When the antenna is provided with a down converter (receiver) the cover may also be arranged to support the receiver.

The provision of the cover also has the advantage of protecting the horn and receiver from the effects of weather.

Snow cannot collect in the reflector and will settle less easily on the cover. moreover, heat generated in the receiver will act to de-ice the cover and to melt any snow thereon.

The cover has the further advantage of reducing distortions caused by wind as the bonding to the reflector increases rigidity.

Preferably the cover is moulded and includes means for fixing the antenna horn at the focus of the ref lector. This has the advantage of obviating the need to make any adjustments to the antenna horn when setting up the antenna.

In a preferred embodiment an expanded polystyrene moulding is included between the ref lector and the cover to give additional rigidity to the antenna and extra support for the cover.

The cover is sealed to the reflector. Any increases in pressure in the gap between cover and reflector are equalised by air leakage through connecting cables. The polystyrene moulding may be bonded to either or both of the cover and reflector. Preferably it is provided with a cavity for receiving the horn and down converter. The cavity is arranged to position correctly the horn and down converter.

It is known for dish antennas to have parabolic reflectors which are a section of a larger parabola chosen such that when the ref lector is mounted against a substantially vertical wall the axis of symmetry of the larger parabola is at an angle to the horizon substantially equal to the angle of elevation above the horizon of the source of the signal to be received by the antenna. The section of the parabola is chosen such that the angle of elevation of the axis of symmetry is between 200 and 300 and preferably 250. This range is chosen for reception of satellite broadcasts in the United Kingdom where the satellite in question is at an elevation of 200 up from the horizon in Northern Scotland and 300 at the southernmost extremity of the UK.

Preferably the antenna reflector embodying the invention is provided with a mounting which allows the angle between the horizon and the axis of reflection of the reflector to be varied within the range of required angles before the antenna is installed.

Preferably this mounting comprises a spherical section on the reverse side of the reflector and a matching spherical mounting plate on the antenna mount. One of the spherical section and the spherical mounting plate is provided with longitudinal slots and the other with locking nuts so that the reflected can be locked at the correct elevation.

To determine the correct angle of elevation a map of the area covered by the satellite footprint (i.e. the U.K.) is provided on the back of the spherical mounting plate. A pointer is located on the back of the spherical surface of the reflector so that the locking nuts can be tightened when the pointer points to the users location on the map.

Preferably the reflector is of square or rectangular outline, the corners may be rounded and the sides bowed outwards.

Preferably, means for varying the azimuth of the antenna are provided which include means for fine tuning and elevation angle. In a preferred embodiment azimuth fixing holes have a limited amount of movement enabling fine tuning of the elevation +/- 2 degrees. This feature has the advantage that the position of antenna can be fined tuned with the antenna in position on a wall. Fine tuning can be made, for example, by the user up a ladder where adjustment of the reflector on the mounting plate would be very awkward.

The invention also provides a dish antenna, ccarrprising a horn, a reflector having a spherical mounting surface, and mounting means for mounting the antenna on a surface, the mounting means oamprising a spherical mounting plate oamplementary to the spherical mounting portion for receiving the mounting portion.

A preferred embodim nt of the invention will now be described with reference to the acccanpanying drawings in which: Figure 1 shows a part-sectional side view of an antenna embodying the invention; and Figure 2 shows a rear view of the antenna reflector and a part of the wall mounting.

The antenna 1 comprises a parabolic reflector 12, a plastics front cover 10, a horn 11 and a down converter 20. Interposed between the reflector and the other components is an expanded polystyrene moulding 25. The cover is bonded to the reflector and to the moulding. The cover houses both the horn and the down converter and so positions the horn at the focus of the parabola. The cover also acts to support the horn and the down converter. The cover is convex and rigid to give additional rigidity to the structure. A spacer (not shown) is interposed, where necessary, between the peripheries of the cover and ref lector to provide a seal around the peripher to the anteanna.

The moulding 25 is provided with cut away portions 26 which assist in locating and supporting the horn and down converter.

The reflector is parabolic and is a section of a larger parabola chosen such that when mounted in a vertical plane, as shown in Figure 1, the axis of symmetry of the parabola is at a predetermined angle to the horizon. In the embodiment illustrated the angle is 25 degrees which corresponds to the angle of elevation of DBS satellite above the horizon in central UK.

The antenna is intended to be mounted against a vertical wall 30 by mounting brackets 13 and 14. punting bracket 13 is fixed to the wall and bracket 14 is connected to bracket 13 by pivot rod 15 whereby bracket 14 can pivot about an axis parallel to the wall 30. pivot rod 15 is provided with a locking nut 16 at each end.

The bracket 14 includes a spherical concave portion 17 which receives a corresponding spherical convex portion 18 located on the reverse of the reflector 12.

As can be seen from Figure 2 the concave portion 17 is provided with vertical slots 19 and the convex portion 18 is provided with locking nuts 27 which serve to lock the antenna to the mounting bracket 14. The reverse side of the concave portion 17 carries a map 22 of the territory covered by the footprint of the satellite and the convex portion 18 of the reflector carries a pointer 23. By a oombination of the correct choice of parabola section for the ref lector and alignment of the pointer with the geographical location of the user the correct elevational angle for receipt of signals can be selected before the antenna is mounted in position on the wall. Some fine tuning may be necessary to ooqpensate for the wall not being exactly vertical and for inaccuracies caused by the alignment of the pointer being only approximate. To compensate for these inaccuracies the holes in the bracket 14 in which pivot rod 15 is mounted are slightly elongated so as to give +/2o of adjustment in elevation angle. Thus, this fine adjustment can be made by releasing the locking nuts 16.

The pivot rod 15 serves as an azimuth adjuster. The antenna is swivelled around the rod until the correct azimuth is located, at which point the locking nuts 16 are tightened.

The reflector may be made of metal or moulded fram plastics material with a metallised reflective coating. When in position as shown in Figure 1, the axis of asymmetry 32 of the parabola of which the reflector 12 is a section points at the transmitting satellite.

Claims

1. A dish antenna comprising a reflector, a horn and a rigid, shaped convex cover, the cover enclosing the horn and being sealed to the periphery of the reflector.

2. A dish antenna according to claim 1, wherein the cover is transparent to the radiation received by the antenna and is bonded to the periphery of the reflector.

3. A dish antenna according to claim 1 or 2 wherein the cover includes a spacer sealed to the periphery of the reflector.

4. A dish antenna according to any of claims 1 to 3 wherein a filler is interposed between the cover and the reflector.

5. A dish antenna according to any of claims 1 to 4, wherein the filler is bonded to the cover and to the reflector to stiffen the antenna.

6. A dish antenna according to claim 4 or 5, wherein the filler is an expanded polystyrene moulding and is provided with means for supporting and positioning the horn.

7. A dish antenna according to any of claims 1 to 6, wherein the cover is arranged to support the horn at the focus of the reflector.

8. A dish antenna according to any of claims 1 to 7, wherein the reflector is parabolic and is a section of a larger parabola chosen such that when the symmetry is mounted against a substantially vertical wall this axis of reflection of the larger parabola is at an angle to the horizon substantially equal to the angle of elevation above the horizon of the source of signal to be received by the antenna the reflector having a spherical mounting portion and the antenna further comprising mounting means for attachment to a mounting surface, the mounting means including a spherical mounting plate oamplementary to the spherical mounting portion for receiving the mounting portion.

9. A dish antenna according to claim 8, wherein one of the mounting portion and the mounting plate is provided with longitudinal slots and the other is provided with locking nuts extending through the slots for adjustment of the angle of elevation of the reflector axis.

10. A dish antenna according to claim 9, wherein the mounting plate and the mounting portion are provided with means for determining the correct angle of elevation of the antenna for the geographical location of the antenna.

11. A dish antenna according to claim 10, wherein the determining means comprises a map on the mounting plate and a pointer on the mounting portion arranged to point at the map.

12. A dish antenna according to claims 8 to 11, wherein the mounting means includes means for adjusting the azimuth angle of the antenna, the azimuth adjusting means including means for fine tuning the angle of elevation of the antenna.

13. A dish antenna, comprising a horn, a reflector having a spherical mounting portion, and mounting means for attachment of the antenna to a mounting surface, the mounting means comprising a spherical mounting plate cmplementary to the spherical mounting portion for receiving the mounting portion.

14. A dish antenna, substantially as herein described with reference to the accompanying drawings.