Radar systems

• US 4,375,640 A
• Filed: 03/10/1980
• Issued: 03/01/1983
• Est. Priority Date: 03/10/1979
• Status: Expired due to Term

• Current Assignee: Siemens Plessey Electronic Systems Limited (BAE Systems Plc)
• Original Assignee: Plessey Handel und Investments AG
• Inventors: Harvey, Denis H.
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US06/128,457
• Time in Patent Office: 1,086 Days
• Field of Search: 343/7.7, 343/5 CF, 343/5 NQ
• US Class Current: 342/93
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242
• CPC Class Codes: G01S 13/5248 combining a coherent MTI processor with a zero Doppler processing channel and a clutter mapped memory, e.g. MTD (Moving target detector), area MTI G01S13/538

Abstract

A radar system comprising a filter with a variable pass band to which radar video signals are fed, data storage means including a main store having a plurality of storage addresses into which data appertaining to the velocity of targets in a plurality of range bearing cells is fed one cell to each address and control signal producing means operative to set the frequency of the filter in dependence upon stored data so that for reception of video signals appertaining to any specified range/bearing cell the frequency of the filter is set in dependence upon the data stored in the address of the main store corresponding to that specified range/bearing cell which appertains to the velocity of any target detected in that range/bearing cell in immediately preceding scans.

Claims

1. A radar system for the detection of non-clutter type moving targets, comprising:

velocity estimator means for producing sequentially, in respect of received radar return signals from objects detected during each complete angular scan, corresponding signals indicative of the velocity of the objects;

averager means responsive to the corresponding signals from the velocity estimator means for providing data appertaining to the average value, over a plurality of angular scans, of the velocity of detected objects;

main store means having a plurality of storage addresses for receiving and storing the data appertaining to the average value of the velocity of said detected objects as sensed at instants in time corresponding to a corresponding number of range/bearing cells, one cell to each address;

moving clutter filter means for receiving radar return signals, having a frequency passband which can be varied in response to control signals, and having an output line; and

control signal producing means for producing control signals for setting the frequency passband of the moving clutter filter means, in dependence upon the data stored in the main store means, to a frequency which reflects an average clutter velocity sensed in a cell during said plurality of scans so that, for the reception of radar return signals in a specified range/bearing cell, the frequency of the moving clutter filter means is set to pass to the output line only those signals having a frequency which corresponds to a velocity which is different from the average clutter velocity sensed in that cell during said plurality of scans, and which could therefore be indicative of a non-clutter type moving target.

2. A radar system as claimed in claim 1, wherein the averager means comprises a buffer store and a summing device connected thereto, and wherein signals derived from the storage addresses in the main store means are provided to the summing device in predetermined proportions with signals derived from the velocity estimator means via the buffer store and appertaining to corresponding range/bearing cells, so that the average value stored at each said storage address is updated from scan to scan.

3. A radar system as claimed in claim 2, wherein the control signal producing means comprises read only memory devices responsive to data stored in the storage addresses of the main store means for providing the control signals which are applied to the moving clutter filter means.

4. A radar system as claimed in claim 3, further comprising a ground clutter filter means for receiving and filtering the radar return signals prior to provision to the velocity estimator means and to the moving clutter filter means.

5. A radar system as claimed in claim 4, further comprising channel selector means for receiving unfiltered radar return signals comprising one channel, for receiving radar return signals via the ground clutter filter means comprising another channel, and for receiving radar return signals via the ground clutter filter means and the moving clutter filter means comprising a third channel, said selector means selecting one of the channels for provision to a display.

6. A radar system as claimed in claim 5, wherein the moving clutter filter means comprises a plurality of serially coupled delay devices provided with radar return signals from the ground clutter filter means, each delay device affording a delay corresponding to a radar pulse repetition period, a plurality of multipliers connected to the delay devices and provided with radar return signals from consecutive radar pulses and with the control signals from the control signal producing means, said plurality of multipliers producing multiplier output signals, and signal combiner means for receiving and combining the multiplier output signals from the multipliers, and providing an output having a frequency response in accordance with the control signals.

7. A radar system as claimed in claim 6, further comprising local oscillator means for providing local oscillator signals, and phase detector means connected thereto for receiving and doppler phase-shifting the radar return signals in accordance therewith so as to provide, from moving targets, doppler phase-shifted signals which are provided to the ground clutter filter means.

8. A radar system as claimed in claim 7, wherein the velocity estimator means comprises a signal processor responsive to relatively delayed signals derived from the delay devices of the moving clutter filter means for providing a signal related to the tangent of doppler phase shifts associated with moving targets, and a read-only memory responsive to the signal provided by the processor for producing a corresponding signal related to phase shift angle, said corresponding signal being fed to the buffer store of the averager means.

9. A radar system as claimed in claim 8, wherein the phase detector means comprises two phase detectors, and further comprising phase quadrature means operatively associated with the local oscillator means for providing quadrature-related outputs to the two phase detectors, thereby to provide I and Q signal channels.

10. A radar system as claimed in claim 9, wherein the main store means includes addresses appertaining to each range/bearing cell for storing data appertaining to the average value of the amplitude of received radar signals, further averager means for deriving the data appertaining to the average value of the amplitude of received radar signals, and a CFAR unit in the said one channel feeding the channel selector means, said CFAR unit including a threshold gate responsive to the stored data appertaining to the average value of the amplitude of received radar signals for adjusting an amplitude threshold above which signals are passed by said threshold gate so as to afford improved signal-to-noise characteristics.