GB2237685A

GB2237685A - Aerial

Info

Publication number: GB2237685A
Application number: GB8922498A
Authority: GB
Inventors: Nigel Henry New
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-10-05
Filing date: 1989-10-05
Publication date: 1991-05-08
Also published as: GB8922498D0

Abstract

A dish aerial for satellite television reception capable of focusing transmissions from several satellites onto a single receptor by the use of several segments of reflector, each focusing the radiation from a single satellite. In order to prevent interference from transmitted radiation of the same frequency from different satellites, the appropriate area of the dish segment may either be shielded by a shutter or the segment may be tilted so as to move the focal point away from the receptor. <IMAGE>

Description

AERIAL FOR THE RECEPTION OF SIGNALS FROM MORE THAN ONE SATELLITE CONCURRENTLV The use of dish aerials to receive transmissions from satellites is established. Such dishes are usually of parabolic form and focus the transmitted microwave or ultra high frequency radio wave to a focal point where it is collected by the receiving equipment.

Originally such units were only used for commercial or military communication and it was of paramount importance that the single channel of communication was well focused such that data was only received or transmitted over a narrow beam to the satellite.

Such units usually had large dishes with powered mechanical systems which enabled the dish to be moved thus enabling it to pick up signals from different points above the Earth.

Satellites are now in orbit to transmit entertainment in the form of television programs. There are at least five such satellite beaming programs to Europe, and more planned.

Each satellite is in a stationary position with respect to the earth. ( Geo-static orbits). Thus such satellite receiving dishes do not require to be moved to follow the orbit of a satellite during transmission. However, it is only possible to pick up signals from a single satellite at a time since the dishes have to be accurately aligned to the satellite in order to receive a signal that is of sufficient strength to give adequate quality, since the satellite transmitter is of low power and is some 25,000 miles away in space.

It is not economically possible for all households to have very expensive and large steerable dishes to enable them to remotely steer the dish from one satellite to another.

In order to change from receiving signals from one satellite to another it is necessary to re-align the dish aerial onto the alternative satellite. This is a difficult task requiring special expertise and equipment.

Rlternatively, it is possible to use two or more separate dish aerials in order to receive signals from these other satellites.

Neither of these solutions are attractive. The first is clearly impractical as a method of changing from one station on one satellite to one on a different satellite. The second is not only expensive, but also takes up large amounts of space and is unlikely to be given planning position in most urban areas. This invention applies to a method of receiving a signal from more than one satellite using a single fixed structure and a single receiver.

The dish is divided into a plurality of segments which may be individually moved in both azimuth and declination at the time of installation, and a receiver which is fixed with respect to the frame of the aerial.

With such a unit it is possible to separately focus the signals from each individual satellite via one of the dish segments onto a single receiving unit.

By way of example, an embodiment of the equipment is now described.

Figure 1 shows a typical dish receiver focusing signals from a satellite onto a receiving sensor.

Figure 2 shows two separate dishes receiving signals from two satellites. Each satellite is at a different position above the earth and thus requires the dish segments to be separately positioned to focus the signals by pointing to different positions in space.

Fig 3 shows the satellite dishes as halt dishes. in such a state they will only collect half the signal of a full dish. However the full strength of the signal can be restored by increasing the diameter Gf the dish by 1.4 times the original dish. Hence if a dish was 20 inches in diameter, in order to receive the same level of signal from half a dish the dish diameter would need to be increased to 28 inches. Rlternatively the signal may well be adequate even if it is reduced by 50% in strength.

Fig 4 shows the two dish halves fitted together such that both satellite signals are received at the same time by a signal receiver unit.

Such a unit may be constructed to concurrently receive the signals from two satellites and, providing the transmission frequencies do not interfere with each other, it will provide a satisfactory solution to receiving signals from two satellites without the problems referred to previously.

This system may be expanded to cover more than two satellites by increasing the number of separately focusable segments.

It should be noted that the plan shape of the reflecting segments need not be a segment of a circle. It can be of any convenient shape so long as its sectional shape allows it to focus the transmitted signals onto the receiving unit. It may therefore be more convenient for cosmetic and structural reasons to have the individual segments of square or triangular shape (or any other shape that better suits the design). Such parts may be mounted in a line, or arranged in any other suitable pattern. Further, the curvature of the segments may be different thus enabling them to focus the incoming signals at different distances from the receiver. By way of example Fig 5 shows a linear array of triangular segments arranged to pick up signals from 4 satellites.

The ability to pick up signals concurrently from more than one satellite with out interference relies on the transmissions not interfering with each other. Rn examination of the transmission frequencies from the satellites show that, in some cases there is no interference thus the receiver can be tuned to different programmes concurrently. However in the case of some transmissions, the frequencies are sufficiently close to cause interference. The interference can be prevented by either shielding the offending receiving segment or temporally rotating it so that it does not focus the unwanted signals onto the receiving unit.

Both the above can be achieved simply. By way of example Fig 6 shows a simple solenoid controlled shutter device and Fig 7 shows a solenoid device for tilting the segment so that its signals no longer reach the receiving unit. In the case of the tilted segment, release of the solenoid will cause spring pressure to return it to its accurately aligned position.

Claims

1. An aerial system for receiving transmissions from satellites or other remote sites consisting of at least 2 separately focusing surfaces onto a single receiver unit.

2. A unit as in claim 1 where the surfaces are fixed with respect to each other.

3. unit as in claim 1 where at least one of the surfaces may be adjusted with respect to the receiver unit in both azimuth and declination.

4. A unit as in the claims above where signals from at least one of the segments may be shielded from the receiver unit, normally to prevent interference of a wanted signal from another concurrently received signal.

5. A unit as in the claims above where one or more of the segments may be tilted or moved to prevent focusing of a potentially interfering signal onto the receiving unit.