GB2264005A

GB2264005A - Tracking system

Info

Publication number: GB2264005A
Application number: GB9201399A
Authority: GB
Inventors: David Scott; Brian Charles Lewis Scott
Original assignee: EDENLIST Ltd
Current assignee: EDENLIST Ltd
Priority date: 1992-01-23
Filing date: 1992-01-23
Publication date: 1993-08-11
Also published as: GB9201399D0

Abstract

A system for correcting rotary phase misalignment of a receiver of polarised electromagnetic radiation signals relative to a source of such radiation, said system comprising: a receiver having a pair of receiver elements (1, 1') each operably adapted to receive a respective polarised component of the polarised electromagnetic radiation signal; a pair of electronic polarotors (2, 2') each operably associated in use with a respective one of said receiver elements (1, 1') to be able to rotate the signal which is received by the element; signal strength sensing means (4, 4') associated in use with the receiver elements (1, 1') to enable the strength of the respective signal received by each receiver element (1, 1') to be sensed; and control means (6, 8) responsive to the difference in sensed signal strengths between each of the receiver elements (1, 1') to correspondingly adjust operation of one or both polarotors. <IMAGE>

Description

TRACKING SYSTEM The present invention relates to a method and means for correcting rotary phase misalignment of a receiver of (non-circularly) polarised electromagnetic radiation relative to a source of such radiation.

The transmissions from a satellite television transmitter, for example, are commonly in a plane or axially (non-circularly) polarised form such that continued good reception of those signals by a suitable receiver is reliant upon maintenance of rotary phase alignment between the source and the receiver - ie the receiver or transmitter must be substantially prevented from rotating relative to each other about an axis extending directly therebetween. A problem therefore arises if for example the transmitter satellite is not geo-stationary or if the satellite is geo-stationary but the receiver is mounted on a moving vehicle or vessel such as a ship. This problem is addressed in the present applicant's co-pending British patent application No 9200700.4 filed on 14th January, 1992 from which the present invention is developed.

According to a first aspect of the present invention there is provided a system for correcting rotary phase misalignment of a receiver of polarised electromagnetic radiation signals relative to a source of such radiation, said system comprising: a receiver having a pair of receiver elements each operably adapted to receive a respective polarised component of the polarised electromagnetic radiation signal; a pair of electronic polarotors each operably associated in use with a respective one of said receiver elements to be able to rotate the signal which is received by the element; signal strength sensing means associated in use with the receiver elements to enable the strength of the respective signal received by each receiver element to be sensed; and control means responsive to the difference in sensed signal strengths between each of the receiver elements to correspondingly adjust operation of one or both polarotors.

Preferably each receiver element is fed the received signal via an orthomode transducer and, where the signal is polarised horizontally and vertically, the receiving elements are angled apart such as to be effectively slightly above or below 90 degrees relative to each other. The receiver elements may be perpendicular to each other and the off-set above or below 90 degrees achieved by operation of one or both polarotors The system suitably further comprises a comparator for automatically comparing the senses signal strength from each respective receiver element with the other to provide a signal representative of the difference between the two signal strengths to the control means.

According to a second aspect of the present invention there is provided a method of correcting rotary phase misalignment of a receiver of polarised electromagnetic radiation signals relative to a source of such signals which method comprises the steps of: providing a system of the first aspect of the present invention; sampling or continuously sensing the respective signal strengths at each receiver element; comparing the respective signal strengths to provide a signal representative of the difference between the signal strengths at each receiver element; and operating the control means in response to the signal representative of the difference to thereby adjust operation of one or both polarotors and thereby compensate for rotary phase misalignment.

A preferred embodiment of the present invention will now be more particularly described with reference to Figure 1 of the accompanying drawings, which is a schematic block diagram of the preferred embodiment of the system of the first aspect of the present invention.

In Figure 1 there is shown a pair of receiver elements 1, 1' of a satellite television transmission receiver.

These receiver elements, 1,1' are angled 90 degrees apart to respectively receive the horizontally and vertically polarised components of a horizontally and vertically polarised satellite television transmission signal.

The receiver elements 1,1' are each fronted by a respective polarotor 2,2' and are each fed the signal received by the receiver via an orthomode transducer 3 or other suitable means.

Each of the two polarotors 2,2' is set to operate to simulate a slight offset from 90 degrees between the respective receiver elements 1 Each receiver element 1,1' has a respective signal strength sensor 4,art associated therewith which may be operated substantially continuously to sense the respective signal strengths or may be operated to sample the respective signal strengths substantially simultaneously at regular intervals.

The signal strengths sensed by the respective signal strength sensors 4,4' are output 5,5' to a comparator 6 for automatically comparing the respective signal strengths and providing an output 7 representative of the difference between the respective signal strengths 5,5'.

The output signal 7 representative of the difference in signal strengths is fed to a controller 8 which outputs control voltages 9,9' to each polarotor 2,2' to adjust the operation of the respective polarotors 2,2' to an extent corresponding to the output 7 of the operator 6 thereby bringing the receiver back into rotary phase alignment with the transmitter should deviation begin to occur.

The system of the present invention provides a simple construction which enables a rapid corrective response to rotary phase misalignment as it occurs. For allround tracking efficiency this system may be used as part of a tracking system as disclosed in British patent application No 91200700.4

Claims

CLAIMS: 1. A system for correcting rotary phase misalignment of a receiver of polarised electromagnetic radiation signals relative to a source of such radiation, said system comprising: a receiver having a pair of receiver elements each operably adapted to receive a respective polarised component of the polarised electromagnetic radiation signal; a pair of electronic polarotors each operably associated in use with a respective one of said receiver elements to be able to rotate the signal which is received by the element; signal strength sensing means associated in use with the receiver elements to enable the strength of the respective signal received by each receiver element to be sensed; and control means responsive to the difference in sensed signal strengths between each of the receiver elements to correspondingly adjust operation of one or both polarotors.
2. A system as claimed in Claim 1, wherein each receiver element is fed the received signal via an orthomode transducer and, where the signal is polarised horizontally and vertically, the receiving elements are angled apart such as to be effectively slightly above or below 90 degrees relative to each other.
3. A system as claimed in Claim 2, wherein the receiver elements are perpendicular to each other and the off-set above or below 90 degrees is achieved by operation of one or both polarotors.
4. A system as claimed in Claim 1, 2 or 3, wherein the system further comprises a comparator for automatically comparing the sensed signal strength from each respective receiver element with the other to provide a signal representative of the difference between the two signal strengths to the control means.
5. A method of correcting rotary phase misalignment of a receiver of polarised electromagnetic radiation signals relative to a source of such signals which method comprises the steps of: providing a system of the first aspect of the present invention; sampling or continuously sensing the respective signal strengths at each receiver element; comparing the respective signal strengths to provide a signal representative of the difference between the signal strengths at each receiver element; and operating the control means in response to the signal representative of the difference to thereby adjust operation of one or both polarotors and thereby compensate for rotary phase misalignment.
6. A system for correcting rotary phase misalignment of a receiver of polarised electromagnetic radiation signals relative to a source of such radiation, the system being substantially as hereinbefore described with reference to the accompanying drawing.