GB2231445A

GB2231445A - Aerial system

Info

Publication number: GB2231445A
Application number: GB8908759A
Authority: GB
Inventors: Anthony Edgar Sale
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-04-18
Filing date: 1989-04-18
Publication date: 1990-11-14
Also published as: GB8908759D0

Abstract

A reflector and horn aerial system which achieves high efficiency without the need for tight manufacturing tolerences and which receives or transmits electromagnetic radiation over a wide range of elevation or azimuth angles without movement of its reflecting surface, comprises a fixed vertically mounted multiple flat plate reflecting aerial 11 and one or more receiving or transmitting horn aerials 12. Mechanisms are disclosed which cause the horns to move on the image curve of the plane of the geostationary earth orbit of fixed satellites as reflected from the multiple flat plate aerial. The multiple flat plate aerial is also capable of receiving or transmitting electromagnetic radiation in more than one direction using one fixed horn. <IMAGE>

Description

MULTIPLE FLAT PLATE AERIAL This invention relates to an aerial system for receiving or transmitting electromagnetic radiation Aerial systems comprising a concave relecting surface with a small horn aerial at the focus of the reflecting surface, are well known for receiving or transmitting high frequency electromagnetic radiation.

Existing designs for reflecting surfaces require manufacture to very close tolerances in order to achieve high efficiency. They have to be very rigid to avoid distortion by wind pressure.

Because of the close tolerences, the small horn has to be positioned very accurately at the focus and rigidly held in place. In order to receive or transmit electromagnetic radiation at different angular positions in azimuth or elevation, the whole reflecting surface together with the small horn, has to be rotated.

According to the present invention, the reflecting surface of the aerial system is made up from more than one flat rectangular or regular shaped reflecting plates, such as hexagonal, each so mounted as to approximate to a concave surface which focusses onto one or more horn aerials. The exact positions of the flat plates are far less critical than for a continuous concave reflecting surface of the same efficiency. The dimensions and shape of the aperture of a horn aerial approximates to those of the surface of a reflecting plate. The multiple plate reflecting surface is rigidly mounted flat against a suitable structural surface such as the wall of a building.

The multiple flat plate reflecting surface allows high efficiency to be maintained for reception or transmission of electromagnetic radiation at large angles away from the normal to the reflecting surface.

The horn is moved relative to the fixed multiple plate reflecting surface in order to receive or transmit electromagnetic radiation at different angular positions in elevation or azimuth.

Alternatively, a number of horns are fixed in positions relative to a fixed single multiple plate reflecting aerial in order to receive or transmit electromagnetic radiation at different angles.

Some plates making up the reflecting surface are moved away from the horn aerial at suitable places in order to minimise the depth of the reflecting surface from the structural surface. The efficiency of the aerial system is preserved by moving such plates by distances equal to multiples of one half the wavelength of the electromagnetic radiation.

Some plates are so positioned as to allow a single horn in conjunction with the multiple plate reflecting surface, to receive or transmit electromagnetic radiation in different angular directions at the same time.

A specific embodiment of the invention will now be described by way of an example, with reference to the accompanying drawings in which: fig 1 shows in perspective an aerial system for the reception of satellite television signals from a number of different satellites; fig 2 shows in perspective a mechanism for causing the horn to move so that signals from different satellites are recieved; fig 3 shows a vertical section through the aerial system together with a different mechanism for causing the horn to move; fig 4 illustrates the relationship between a plate dimensions and the horn aerial aperture dimensions.

Refering to fig 1, the satellite receiving aerial system comprises a matrix of flat rectangular reflecting plates 11, mounted rigidly against the vertical wall of a building such that the wall faces in the general direction of the satellites. Each plate is adjusted in position to reflect into the horn aerial 12, that part of the incoming satellite signal which it intercepts.

Refering to fig 2, the horn 22 is supported in front of the multiple plate reflector 21, at the bottom by bracket 23, pivot 24 and the rigid strut 25. The horn 22 is supported in the verticle plane by rope or flexible wire 16. In order to cause the horn to move to positions in front of the reflecting plates corresponding to the images of different satellites, the vertical support wire is one continuous wire passing over pulleys 27 and 28. The position of pulleys 27 and 28 with respect to the reflecting plates, the length of bracket 23 and the length of the rigid rod 25, are chosen so that by pulling on wire 26 between the pulleys 27 and 28, at 29, the horn follows the image of the plane of the geostationary orbit in which the satellites reside.

Refering no .o fig 3, this shows a rertica) ross-section of the aerial system. In fig 3, 31 indicates the vertical wall against which the reflecting aerial is mounted. 32 is a wooden or plastic baseboard to which the matrix of flat plates 33, are attached.

In a different mechanism, the horn aerial 34 is supported by bracket 35 and the rigid strut 37 attached to pivots 36. By suitable choice of the length of strut 37 and of the positions and angle of pivots 36, with respect to the flat plates 33, the horn can be constrained to follow the image of the plane of the geostationary orbit in which the satellites reside.

Fig 3 also shows the setting back of some plates as at 38, in order to reduce to a minimum the depth of the reflecting surface from the structural support 31.

The flat reflecting plates can be metal or wood or plastic coated with a thin metallic film. The plates are attached to the baseboard by screws which are also used to adjust the slope and position of the plates. Alternatively the metal or foil plates are embedded at the correct angles and positions in an expanded plastic such as polythene which is then wrapped in a weatherproof covering and attached to the structural support.

Refering to fig 4, this shows in schematic form the relationship between one reflecting plate 42, the incoming satellite signal 41, the reflected signal 44 and the horn aerial 45. The high efficiency of the multiple plate reflector derives from the effect of an interference pattern caused by the finite width of the plate 42, compared to the wavelength of the incoming satellite signal 41. By careful choice of the plate width with respect to the signal wavelength, the horn 45 can receive a signal strength greater than that from an infinite reflecting surface in place of plate 42. In addition, the field strength at the edges of the plate can be nearly zero so that it is immaterial whether adjacent plates touch or not.

Claims

1. An aerial system for receiving or transmitting eletromagnetic waves said aerial system comprising more than one flat rectangular or regular shaped reflecting plate and single or multiple receiving or transmitting horn aerials with aperture dimensions approximately equal to the surface dimensions of a plate

2. An aerial system as in claim 1 with the flat plates positioned approximately on a concave surface with a receiving or transmitting horn at the focus of the concave surface.

3. An aerial system as in claim 2 with the plates set back from the concave surface at such places as may allow the depth of the multiple plate aerial to be kept to a minimum.

4. An aerial system as in claims 1, 2 or 3 wherein some plates are so positioned as to allow a single fixed horn aerial to receive or transmit electromagnetic radiation at the same time from or to different azimuth or elevation angles relative to the normal to the fixed multiple plate aerial.

5. An aerial system as in claims 1, 2, 3 or 4 wherein the single or multiple horns are adjustable in position in front of a rigidly mounted multiple plate aerial, in order to receive or transmit electromagnetic radiation over a wide range of azimuth and elevation angles relative to the normal to the multiple plate aerial.

6. An aerial as in claim 5 such that the movement of the horn aerials is constrained by some mechanical means to be on the image curve of the geostationary orbit plane as reflected from the multiple plate aerial.