GB2278731A - Monopulse radar systems - Google Patents

Abstract

An antenna arrangement for a monopulse radar tracking system in which a 4-horn cluster is used exclusively for receiving and a fifth horn, incorporated centrally within the cluster and having the same boresight, is used exclusively for the transmit signal. The antenna may be arranged for amplitude comparison target tracking with the four horns having axes diverging from a common point. <IMAGE>

Description

Monopulse Radar System This invention relates to a monopulse radar tracking system particularly, but not exclusively, for use with a cassegrain reflector antenna.

A monopulse tracking radar will conventionally use a 4-horn cluster at the focus of the antenna for reception of signals. Angular signals, i.e. signals indicating target angle off boresight, are extracted by following the horn cluster with a comparator device.

This uses combining techniques to produce a sum signal plus azimuth and elevation difference signals. The same horn cluster is used for transmission by injecting signals into the sum port of the comparator by way of a duplexer to separate the transmit and receive paths.

Such systems suffer from leakage of the high power transmit signal through the duplexer to the receiver. Consequently protection devices, e.g. transmit/receive switches, are necessary to protect the signal detector diodes. Such arrangements are expensive in requiring specific components, and in addition produce RF losses in both tranmit and receive.

According to the present invention, in a monopulse radar tracking system comprising a 4-horn cluster antenna arranged in a square array for receiving target signals, comparator means coupled to the four horns to provide a sum signal, an azimuth difference signal and an elevation difference signal, processing means for producing from the sum and difference signals azimuth and elevation target angles off the antenna boresight, the system further comprises a transmitting horn antenna located centrally between the 4 receiving horns and having a common boresight with them, and a radar transmitter oscillator coupled to the transmitting horn antenna.

The 4-horn cluster antenna may be arranged for amplitude comparison target tracking, the four horns having individual axes diverging from a common point.

The transmitting horn antenna is preferably of circular cross section for minimum blockage.

The cluster antenna and the transmitting antenna may constitute the feed of a cassegrain reflector antenna.

An antenna for a monopulse radar tracking system in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings of which: Figure 1 is a head-on view of the antenna array; and Figure 2 is a diagrammatic side view of the antenna and associated comparator device.

Figure 1 shows 4 receiving horns A, B, C, and D in a 'square' array, each horn being of very approximately conical form terminating at the rear end in waveguide shown in Figure 2.

The front corners of the 4 horns are cut-away to accommodate a circular transmitting horn E whose mouth is in the same plane as the mouths of the other horns A-D. This transmitting horn E is symmetrically positioned between the receiving horns and thus has a common boresight with them.

As shown in Figure 2, the receiving horns are coupled to a comparator which produces, in known manner, a sum signal and azimuth and elevation difference signals. In conventional monopulse systems the transmit signal, derived from a local oscillator, is fed to the sum channel of the comparator for distribution to the 4 horns A-D.

This has to be by way of a duplexer in an attempt to prevent the high power transmit signal from reaching the receiver directly.

In this embodiment the fifth horn E is coupled by waveguide to the transmit oscillator (not shown), the receiving horns serving as receivers exclusively. Thus there is no circuit coupling between the transmit path and the receive path.

The absence of a duplexer and other receiver protection devices reduces the sytem costs and improves the RF performance.

Further, the separation of transmit and receive channels eases problems of matching of the sum and difference channels.

The invention is of particular value in application to circularly polarized systems.

While the antenna arrangement described could be of 'stand-alone' type, it is primarily intended for use with a cassegrain reflector system.

Claims (5)

1. A monopulse radar tracking system comprising a 4-horn cluster antenna arranged in a square array for receiving target signals, comparator means coupled to the four horns to provide a sum signal, an azimuth difference signal and an elevation difference signal, processing means for producing from the sum and difference signals azimuth and elevation target angles off the antenna boresight, the system further comprising a transmitting horn antenna located centrally between the 4 receiving horns and having a common boresight with them, and a radar transmitter oscillator coupled to the transmitting horn antenna.

2. A radar system according to Claim 1, wherein said 4-horn cluster antenna is arranged for amplitude comparison target tracking, the four horns having individual axes diverging from a common point.

3. A radar system according to Claim 1 or Claim 2, wherein said transmitting horn antenna is of circular cross section.

4. A radar system according to any preceding claim wherein said cluster antenna and said transmitting antenna constitute the feed of a cassegrain reflector antenna.

5. A radar system antenna substantially as hereinbefore described with reference to the accompanying drawings.

5. A radar system antenna substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A monopulse radar tracking system comprising a 4-horn cluster receive only antenna arranged in a square array for receiving target signals, comparator means coupled to the four horns to provide a sum signal, an azimuth difference signal and an elevation difference signal, processing means for producing from the sum and difference signals azimuth and elevation target angles off the antenna boresight, the system further comprising a transmit only horn antenna located centrally between the 4 receiving horns and having a common boresight with them, and a radar transmitter oscillator coupled to the transmit only horn antenna.

2. A radar system according to Claim 1, wherein said 4-horn cluster antenna is arranged for amplitude comparison target tracking, the four horns having individual axes diverging from a common point.

3. A radar system according to Claim 1 or Claim 2, wherein said transmit only horn antenna is of circular cross section.

4. A radar system according to any preceding claim wherein said cluster receive only antenna and said transmit only antenna constitute the feed of a cassegrain reflector antenna.