RADAR SYSTEM

• US 20090295620A1
• Filed: 06/19/2009
• Published: 12/03/2009
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Blighter Surveillance Systems Ltd
• Original Assignee: Plextek Ltd.
• Inventors: SPREADBURY, David, RADFORD, Mark, GREENDALE, Steve
• Granted Patent: US 7,876,262 B2
• Time in Patent Office: Days
• US Class Current: 342/28
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242

Abstract

Electronically steered radar systems such as frequency scanning radars are particularly suitable for detecting and monitoring slow moving, ground-based targets. So-called crawler radar systems are intended for detection of targets that deliberately attempt to avoid detection by keeping low and by moving slowly. Disclosed is a radar system which includes an electronically steered antenna and a receiver arranged to process signals received from a target located at a distance from the radar system so as to identify a Doppler frequency associated with the target. The antenna stares at, rather than glides past, the target surrounding clutter. This means that the spectral spreading of static ground clutter associated with mechanical radar systems can be eliminated, overcoming one of the shortcomings of mechanical radar systems that would otherwise render a crawler radar system unsuitable for Doppler processing.

Claims

1. A frequency modulated continuous wave radar system capable of detecting a slow moving target, the radar system comprising an electronically steered antenna and a receiver arranged to process signals received from a target located at a distance from the radar system so as to identify a Doppler frequency associated with the target,

the receiver comprising:

a signal processor operable to derive frequency tone data corresponding to a plurality of range gates;

a low frequency blocking filter; and

a Doppler processor for deriving Doppler frequency data,

wherein said low frequency blocking filter is arranged to identify an average magnitude of said frequency tone data associated with a given range gate and to subtract the identified average magnitude from respective said signals prior to processing by the Doppler processor.

2. A frequency modulated continuous wave radar system according to claim 1, wherein the radar system is capable of detecting a target having a radar cross section area of less than 0.2 m² and the electronically steered antenna is arranged to transmit signals in a plurality of directions so as to steer a beam over an angular extent, the electronically steered antenna being arranged to transmit signals in a given one of the plurality of directions for a period, said period having a duration at least ten times that of a corresponding period suitable for Doppler processing of a target having a radar cross section area of 1 m² located at said distance from the radar system.

3. A frequency modulated continuous wave radar system according to claim 2, wherein the receiver comprises a Doppler Fast Fourier Transform (FFT) device for deriving said Doppler frequency data.

4. A frequency modulated continuous wave radar system according to claim 3, including a Range Fast Fourier Transform (FFT) device operable to derive said frequency tone data corresponding to a plurality of range gates.

5. A frequency modulated continuous wave radar system according to claim 4, the receiver comprising signal processing means arranged to process said tones so as derive data indicative of movement of said target, and to transmit said derived movement data to a display means, said display means being located remote from said radar system.

6. A frequency modulated continuous wave radar system according to claim 1, wherein the electronically steered antenna comprises a frequency scanning antenna and the radar system comprises a frequency generator, the frequency generator being arranged to generate a plurality of sets of signals, each set having a different characteristic frequency, the frequency generator comprising a digital synthesiser arranged to modulate a continuous wave signal of a given characteristic frequency by a sequence of modulation of patterns whereby to generate a said set of signals.

7. A frequency modulated continuous wave radar system according to claim 1, wherein the electronically steered antenna comprises a phased antenna having a plurality of antenna elements, the antenna elements being spatially arranged with respect to one another and being operable to transceive signals, wherein the radar system comprises delay circuitry arranged to apply an amount of delay to the signals transceived by antenna elements.

8. A frequency modulated continuous wave radar system according to claim 1, wherein the electronically steered antenna comprises a phased antenna having a plurality of antenna elements, the antenna elements being spatially arranged with respect to one another and being operable to transceive signals, wherein the radar system comprises phase shift circuitry arranged to apply an amount of phase shift to the signals transceived by antenna elements.