GB2184627A

GB2184627A - Target identification system

Info

Publication number: GB2184627A
Application number: GB08531467A
Authority: GB
Inventors: Jagjit Singh Kang
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1985-12-20
Filing date: 1985-12-20
Publication date: 1987-06-24

Abstract

A radar target identification system which operates analogously to a hologram comprises a radar transmitter (1) spaced apart by some distance from a receiver (5), the transmitter having a transmission antenna arrangement for transmitting microwave energy directly to an aerial array of the receiver (5) and to a target (3) so that the aerial array (5) of the receiver receives microwave energy reflected from the target (3) and directly radiated microwave energy, the aerial array (5) which feeds the receiver comprising a planar array of individual aerial elements (7), each individual element (7) being connected to a fast Fourier transform unit (9) whereby an interference pattern present at the aerial is processed for providing an electronic representation of the target (3) shape. The electronic representation may be displayed on a VDU (11) or compared with previously stored information in a comparator (12). <IMAGE>

Description

SPECIFICATION Target Identification System This invention relates to a target identification system.

In the detection and identification of a target object by a radar technique, the object surface is used to reflect an incident beam of microwave energy from a transmitter back to a receiver. The signal obtained at the receiver is then used to detect the target object. The received signal, however, does not usually give good resolution of the shape of the object so an identification of the target object still remains something of a problem.

The present invention was devised to provide a system of detection of a target object in a way that would give a better resolution of the object shape.

This can enable a rapid identification of the object to be achieved.

According to the invention, there is provided a radar target identification system comprising a radar transmitter spaced apart by some distance received from a receiver, the transmitter having a transmission antenna arrangement for transmitting microwave energy directly to an aerial array of the receiver and to a target so that the aerial array of the receiver receives microwave energy reflected from the target and directly radiated microwave energy, the aerial array which feeds the receiver comprising a planar array of individual aerial elements, each individual element being connected to a fast Fourier transform unit whereby an interference pattern present at the aerial is processed for providing an electronic representation of the target shape.

Preferably, each individual element of the aerial array is a microwave receiver, an image intensifier or a solid state detector. Each individual element of the array may be associated with a capacitor effective for storing a level of electrical energy representative of the interference pattern present at that part of the array.

The fast Fourier transform unit may have an output providing signals to a visual display unit to facilitate a visual identification of the target shape.

In a different embodiment, the fast Fourier transform unit may have an output providing signals to a comparator device whereby the target information can be compared with information held in a memory store associated with the comparator, for automatic identification of the target object.

By way of example, a particular embodiment of the invention will now be described with reference to the accompanying drawing which shows, somewhat diagrammatically, a target identification system.

In the technique of holography, an object being photographed is illuminated by a laser, and the wavefront scattered from it falls on a fine-grain photographic plate, together with a wavefront derived from a separate beam obtained directly from the laser. The present invention employs a technique similar to that of holography but instead of using optical wavelengths of light, a -microwave transmission is used.

The drawing shows a microwave transmitter 1 which produces a first microwave beam 2 which is incident on a target 3. The target 3 surface reflects the beam 2 to create a reflected beam 4 and this is directed onto an aerial array 5. At the surface of the aerial array 5, the reflected beam 4 forms an interference pattern with a second microwave beam 6 which falls directly on the array 5 from the transmitter 1.

The interference pattern is formed by the interaction between the two wavefronts, one being derived from the beam 4 scattered from the surface of the target 3 and the other from the second microwave beam 6 received directly from the transmitter 1.

The interference pattern is produced on the surface of the aerial array 5 and this surface is constituted by a planar array of individual aerial elements 7. For the sake of clarity in the drawing, the aerial array 5 has been simplified to a great extent, and only a small number of the individual elements 7 have been shown. In a practical construction, there would of course be hundreds or thousands of these elements 7.

Each element 7 is a microwave receiver and this is connected to a capacitor 8 capable of storing an electrical signal representative of the signal received by the element 7. The whole array of capacitor 8, each one of which is coupled to an element 7, is thus capable of storing an energy distribution pattern which is representative of the interference pattern on the aerial array surface. Again, for simplicity in the drawing, this shows only a single row of the capacitor 8.

Each capacitor 8 is connected as an input to a fast Fourier transform unit 9 which is arranged to process the information received and display a suitable output on a visual display unit 11. The resulting visual patterns which are produced on the display unit 11 are capable of being interpreted by a skilled operator and will then give information enabling an identification of the shape of the target 3 to be made.

In an alternative way of treating the information produced by the fast Fourier transform unit 9, this has an output which is fed to a comparator 12, and the comparator 12 is also capable of retrieving target shape information which has been generated previously and is retained in a memory store 13.

When the comparator 12 detects a similarity between the information from the transform unit 9 and that from the memory store 13, an appropriate output indicating the target shape will be displayed and an output device 14. This arrangement will thus give an automatic indication of the target shape.

The foregoing description of an embodiment of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, instead of the aerial elements 7 being microwave receivers, the elements could alternatively be image intensifiers or solid state detectors.

Claims

1. A radar target identification system, comprising a radar transmitter spaced apart by some distance from a receiver, the transmitter having a transmission antenna arrangement for transmitting microwave energy directly to an aerial array of the receiver and to a target so that the aerial array of the receiver receives microwave energy reflected from the target and directly radiated microwave energy, the aerial array which feeds the receiver comprising a planar array of individual aerial elements, each individual element being connected to a fast Fourier transform unit whereby an interference pattern present at the aerial is processed for providing an electronic representation of the target shape.

2. A target identification system as claimed in Claim 1, in which each individual element of the aerial array is a microwave receiver, an image intensifier or a solid state detector.

3. A target identification system as claimed in Claim 1 or Claim 2, in which each individual element of the array is associated with a capacitor effective for storing a level of electrical energy representative of the interference pattern present at that part of the array.

4. A target identification system as claimed in any one of Claims 1 to 3, in which the said Fourier transform unit has an output providing signals to a visual display unit to facilitate a visual identification of said target shape.

5. A target identification system as claimed in any one of Claims 1 to 3, in which the said Fourier transform unit has an output providing signals to a comparator device whereby the target information can be compared with information held in a memory store associated with the comparator, for automatic identification of said target.

6. A target identification system substantially as hereinbefore described with reference to the accompanying drawing.