GB2065377A

GB2065377A - A combined radar communication system

Info

Publication number: GB2065377A
Application number: GB7941955A
Authority: GB
Original assignee: MARCONU CO Ltd
Current assignee: MARCONU CO Ltd
Priority date: 1979-12-10
Filing date: 1979-12-10
Publication date: 1981-06-24
Also published as: GB2065377B

Abstract

In known systems where a missile is tracked by a monopulse radar and is communicated with by another microwave system it is known to use two main reflectors, one for the tracking system and one for the communication system. The invention provides a single main reflector 1 having, at its focal point a feed 6 for the communications system which transmits messages to and receives messages from the missile. A secondary reflector 22 between the reflector 1 and the feed 6 provides the reflector 1 with a second focal point at which a feed 14 belonging to a monopulse tracking system is located. The tracking system and the communication system operate at different frequencies and the secondary reflector 22 is designed so as to transmit frequencies at which the communication system operates and to reflect frequencies at which the tracking system operates. By employing the invention it is possible to avoid the need for two reflectors 1. <IMAGE>

Description

SPECIFICATION A communication system This invention relates to a communication system.

The invention arose when considering problems involved in the design of radar systems for tracking a missile and for communicating with the missile for example to adjust its course. Hitherto such systems have required two reflectors: one for tracking and one for use as a communications channel. The invention enables a single main reflector to be used for both functions.

The invention provides a communication system for transmitting to and/or receiving from a remote location first and second electromagnetic signals falling within respective first and second signal types, the arrangement comprising: a focussing element which reflects the first and second signals and has a first focal point; a reflector located between the focussing element and the first focal point, the reflector being transmissive to the first signals and reflective to the second signals thereby providing the focussing element with a second focal point for the second signals; a first transmitting and/or receiving apparatus arranged to feed the first signals to, and receive them from, a first signal feed located at or adjacent to the first focal point; and a second transmitting and/or receiving apparatus arranged to feed the second signals to, or to receive them from, a second signal feed located at or adjacent the second focal point.

The invention also provides a system for tracking a moving object and communicating with it comprising a focussing device having a first focal point; a reflector or beam splitter which provides the focussing device with a second focal point; and two feeds associated with respective focal points, one of the said feeds being connected to a system for tracking the object and the other feed being connected to a system for transmitting instructions to the object and/or for receiving information transmitted by it.

The first and second signal types will normally be distinguished from each other by belonging to different frequency ranges; in which case the reflector is frequency discriminating. Where, as is preferred, the system operates at microwave frequencies, the aforementioned reflector may comprise a special pattern of electrically conductive material designed to make the reflector frequency discriminating. A suitable pattern is known as the Jerusalem Cross, this being described for example by Anderson in a paper entitled "On the Theory of Self-Resonant Grids" published in the Bell System Technical Journal 1 975, volume 54, pp 1725-1731. The Jerusalem Cross reflector behaves as a filter which transmits certain frequencies and reflects other frequencies depending on various dimensions of the pattern.This reflector need not necessarily be flat. It may be convex or concave depending on the position in which it is most convenient to locate the second signal feed.

It has previously been mentioned that the invention arose in connection with a combined tracking and communication system for a missile. Accordingly, a preferred feature of this invention is that the focussing element, the said reflector and the feeds are carried by an adjustable mounting, one of the said ap- paratus" being a tracking receiver which adjusts the mounting according to the direction from which radiation is received, and the other "apparatus" being adapted to conduct messages to and from the missile.

One example of how the invention may be performed will now be described with reference to the accompanying drawings in which Figure 1 is a very schematic illustration, partly in section and partly in elevation, or a radar transmitting and receiving apparatus constructed in accordance with the invention and designed for tracking and guiding a missile; and Figure 2 illustrates, in detail, a small part of a reflector indicated at 22 on Fig. 1.

The illustrated system comprises a focussing element in the form of a parabolic dishshaped reflector 1 which is offset from the axis of the parabola. This offset configuration is a conventional technique which avoids obstruction of the radiated and received beams.

The reflector 1 is carried by a mounting member 2. The member 2 is pivotted about a horizontal axis to two lugs 3A (only one of which is illustrated) fixed to a toothed wheel 3. The wheel 3 has a vertical shaft 3B received by a bearing block 4. This arrangement enables the mounting member 2 to be adjusted in azimuth and elevation.

A cantilever 5, fixed to the mounting member 2, supports a feed 6 at a focal point of the reflector 1. The feed 6 supplies control signals to a missile, e.g. for adjusting the course thereof and also receives data from the missile. During transmission a diverging beam is, at times, transmitted from the feed 6 towards the lower half of the reflector 1. This produces a parallel beam after reflection from the reflector 1. This situation is changed during the course of transmission so that, at other times, a diverging beam is transmitted from the feed 5 in a direction such as to illuminate the upper half of the reflector 1 thereby producing a parallel beam at an upper level.Suitable control circuitry may be provided, as is known per se, so as to select between the upper or lower level beams or a combination of both of them depending on which of these possibilities is least affected by noise.

Selection between the two beams is ef fected by a 3dB hybrid coupler 7 having two input ports 8 and 9 and two output ports 10 and 11. The output ports 10 and 11 are connected to respective horns 1 2 and 1 3 located adjacent to each other and forming part of the feed 6. The circuit 7 has, as is well known, characteristics such that an input at port 8 is split into two parts of identical frequency. These parts appear at outputs 10 and 11 in phase quadrature, the phase of the energy at port 10 leading that at port 11 by 90 > . If an input is applied to port 9 the energy is likewise split between ports 10 and 11 but in a manner such that the phase of the energy at port 10 lags that at port 11 by 90'.

When the energy at 10 leads that at 11 the effect at the horns 1 2 and 1 3 is to produce a downward squint, i.e. to deflect the direction of radiation from the optical axis (illustrated in broken lines) towards the lower half of the reflector 1. Likewise, when the phase at 10 lags that at 11 the beam is deflected upwardly towards the top half of the reflector 1.

The foregoing description relates to the system when operating as a transmitter. When operating as a receiver similar considerations apply. Radiation received by the lower half of the reflector 1 arrives at the horn 1 2 with a 90 phase lead compared with that at 1 3 causing the 3dB coupler 7 to produce an output primarily at port 8. Likewise, radiation received by. the upper half of the reflector 1 is incident on horn 1 3 with a 90G phase lead with respect to horn 1 2. The coupler 7 accordingly produces an output primarily at port 9. The receiving circuitry (not shown) is designed so that it can switch between ports 8 and 9 so as to receive whichever signal is least effected by noise, or a combination of the two signals.

The transmitting arrangement consisting of components 7, 1 2 and 1 3 receives microwave energy at one particular, first, frequency which is used for transmitting com- riand messages to the missile and for receiving data from the missile. Tracking of the missile is performed by a monopulse system operating at a second frequency. The monopulse system has an input/output feed 14 comprising four horns as illustrated schematically in Fig. 1 supported on the mounting member 2. This monopulse system operates conventionally, in that the horns 14 are connected to a transmitting, receiving circuit 1 5.

This produces outputs on a line 1 6 and 1 7 which represent the azimuth and elevation of the missile relative to the boresight 1 8 of the system. The signal on line 16 controls a motor 1 9 which rotates a toothed wheel 20.

This meshes with wheel 3 to adjust the azimuth. The signal on line 1 7 controls a motor 21 which rotates a shaft fixed to the mounting 2 to adjust the elevation of the boresight 18.

Radiation transmitted from the feed 14 is directed to a convex reflector 22 which consists of a transmissive substrate having a convex surface facing the reflector 1, on which convex surface is deposited a pattern of electrically conductive material. Part of the reflector 22 is illustrated in Fig. 2 where the substrate is shown at 23. As can be seen from Fig. 2 the conductive material 24 forms a grid of perpendicular lines and a cross in each space formed between the lines. Each arm of the cross is in the form of a letter T. It is well known in the field that a gridded Jerusalem Cross pattern such as illustrated in Fig. 2 acts as a filter allowing certain frequent cies to pass through it and reflecting other frequencies.Thus, relatively high frequencies emitted from and received by feed 14 and the associated circuitry are reflected from the reflector 22 so as to provide the focussing device 1 with a second focal point positioned centrally between the horns of the monopulse feed 14. Conversely, relatively low frequencies emitted and received by the feed 6 and associated circuitry, pass through the reflector 22.

Thus the reflector 22 acts as a beam splitter enabling radar apparatus to be directed along and received from the same path between the missile and the common reflector 1. Consequently, the cost of a second main reflector is avoided and the communication signals from the feed 6 are automatically aligned with the direction of the missile.

It will be appreciated that this invention is not limited to systems which employ monopulse tracking or which employ squint to achieve spacial diversity. It is also pointed out that, whilst the embodiment shown in Fig. 1 employs an offset parabolic reflector, the invention is also applicable to other systems in which other focussing devices are used.

Claims

1. A communication system for transmitting to and/or receiving from a remote location first and second electromagnetic signals falling within respective first and second signal types, the arrangement comprising: a focussing element which reflects the first and second signals and has a first focal point; a reflector located between the focussing element and the first focal point, the reflector being transmissive to the first signals and reflective to the second signals thereby providing the focussing element with a second focal point for the second signals; a first transmitting and/or receiving apparatus arranged to feed the first signals to, and receive them from, a first signal feed located at or adjacent to the first focal point; and a second transmitting and/or receiving apparatus arranged to feed the second signals to, or to receive them from, a second signal feed located at or adjacent the second focal point.

2. A system according to claim 1 in which the first and second signal types are different frequency ranges and in which the said reflector is frequency discriminating.

3. A system according to claim 1 or 2 in which the focussing element, the said reflector and the feeds are carried by an adjustable mounting and in which one of the said apparatus is a tracking receiver which adjusts the mounting according to the direction from which the radiation is received.

4. A system according to claim 3 in which the other said apparatus is adapted to transmit and/or receive messages to and/or from an object in the said direction.

5. A missile guidance and tracking system according to claim 4 in which the said other apparatus is adapted to transmit messages to a missile and in which the missile is adapted to change or correct its course in response to the said messages.

6. A system according to any preceding claim in which the said focussing element is reflective.

7. A system according to any preceding claim for transmitting and/or receiving microwave signals in which the said reflector comprises a pattern of electrically conductive material.

8. A missile tracking and guidance system substantially as described with reference to the accompanying drawings and substantially as illustrated therein.

8. A system according to any preceding claim in which the said reflector has a convex reflective surface facing the focussing element.

9. A system for tracking a moving object and communicating with it comprising a focussing device having a first focal point; a reflector or beam splitter which provides the focussing device with a second focal point; and two feeds associated with respective focal points, one of the said feeds being connected to a system for tracking the object and the other feed being connected to a system for transmitting instruction to the object and/or for receiving information transmitted by it.

10. A missile tracking and guidance system substantially as described with reference to the accompanying drawings and substantially as illustrated therein.

CLAIMS ( 1 5 Jan 1 981 )

1. A system for tracking a moving object and communicating with it comprising a focussing device having a first focal point; a beam splitter which provides the focussing device with a second focal point; and two feeds associated with respective focal points, one of the said feeds being connected to a system for tracking the object and the other feed being connected to a system for transmitting instruction to the object and/or for receiving information transmitted by it.

2. A system according to claim 1 in which the two said systems operate at different frequencies and in which the beam splitter is a frequency discriminating reflector.

3. A system according to claim 1 or 2 in which the focussing device, the said beam splitter and the feeds are carried by an adjustable mounting and in which the system for tracking the object adjusts the mounting according to the direction from which radiation is received from the object.

4. A missile guidance and tracking system according to any preceding claim which the system for transmitting instructions to the object is adapted to change or correct its course in response to the said instructions.

5. A system according to any preceding claim in which the said focussing device is reflective.

6. A system according to claim 2 for transmitting and/or receiving microwave signals in which the said reflector comprises a pattern of electrically conductive material.

7. A system according to claim 2 in which the said reflector has a convex reflective surface facing the focussing element.