Radar clutter suppression system

• US 9,213,088 B2
• Filed: 05/17/2012
• Issued: 12/15/2015
• Est. Priority Date: 05/17/2011
• Status: Active Grant

• Current Assignee: Navico Incorporated (Brunswick Corporation)
• Original Assignee: Navico Holding A.S. (Brunswick Corporation)
• Inventors: Mowbray, Robert Stephen, Phillips, Roger
• Primary Examiner(s): BYTHROW, PETER M
• Application Number:
  US13/474,289
• Publication Number:
  US 20120293361A1
• Time in Patent Office: 1,307 Days
• Field of Search: 342159-164, 342/205
• US Class Current: 1/1
• CPC Class Codes: G01S 13/02 Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
• CPC Class Codes: G01S 13/5242 with means for platform motion or scan motion compensation, e.g. airborne MTI
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242
• CPC Class Codes: G01S 7/2922 by using a controlled threshold
• CPC Class Codes: G01S 7/2925 by using shape of radiation pattern
• CPC Class Codes: G01S 7/2927 by deriving and controlling a threshold value
• CPC Class Codes: G01S 7/34 Gain of receiver varied automatically during pulse-recurrence period, e.g. anti-clutter gain control
• CPC Class Codes: G01S 7/414 Discriminating targets with respect to background clutter

Abstract

Sidelobe suppression methods and systems for use in processing radar video streams generated by rotational radar antenna scanners. The sidelobe suppression methods function in parallel with traditional Sensitivity Control (SC) processing by selectively reducing sensitivity where necessary depending on sidelobe suppression schemes that can be either directional, omni-directional (non-directional), or a combination of these.

Claims

1. A method of suppressing sidelobe clutter in a radar signal processing system that receives a radar video stream from a radar antenna scanner and applies Sensitivity Control (SC) processing to the radar video stream based on an SC threshold profile that defines an echo return intensity threshold over range, the method implemented by a processor of the radar signal processing system and comprising the steps of:

receiving the radar video stream from the radar antenna scanner;

determining estimates of the sidelobe clutter contribution levels (herein;

sidelobe estimates) based on a buffer of the radar video stream and an antenna beam pattern response model of the radar antenna stored in memory of the radar signal processing system, the stored antenna beam pattern response model representing the radar antenna response level across an azimuthal range centered about a main beam of the radar antenna;

selectively modifying the SC threshold profile based on the determined sidelobe estimates to selectively reduce the sensitivity of the SC processing based on the determined sidelobe estimates; and

applying SC processing to the radar video stream based on the selectively modified SC threshold profile to generate an SC processed radar video stream having reduced sidelobe clutter.

2. A method according to claim 1 wherein the radar video stream represents the echo return intensities detected by the radar antenna scanner during 360 degree scanner sweeps, sampled in azimuth and range, and wherein the radar video stream comprises a stream of azimuthal vector data, each azimuthal vector representing the echo return intensities at a number of range samples for an azimuthal direction in the radar antenna scanner sweep.

3. A method according to claim 2 wherein determining sidelobe estimates comprises determining sidelobe estimates for each new azimuthal vector in the radar video stream such that each azimuthal vector has corresponding sidelobe estimates.

4. A method according to claim 3 wherein determining sidelobe estimates for each azimuthal vector comprises, for each azimuthal vector, determining the sidelobe estimates based on a buffer of the radar video stream centered about the azimuthal vector.

5. A method according to claim 4 wherein determining the sidelobe estimates for each azimuthal vector comprises, for each azimuthal vector, generating a sidelobe contribution vector representing the sidelobe estimates for the azimuthal vector, the sidelobe contribution vector comprising estimates of the maximum sidelobe contribution levels at each range sample calculated based on the buffer of the radar video stream and the antenna beam pattern response model.

6. A method according to claim 5 wherein determining the sidelobe estimates for each azimuthal vector comprises, for each azimuthal vector, generating a set of individual candidate sidelobe levels for each range by applying the antenna beam pattern response model to the cross-range samples from each azimuthal vector within the azimuthal buffer range, and generating the sidelobe contribution vector by selecting at each range sample the maximum of the calculated set of individual candidate sidelobe levels for the range.

7. A method according to claim 2 wherein selectively modifying the SC threshold profile comprises increasing the threshold levels of the SC threshold profile in range regions where the determined sidelobe estimates exceed the original threshold levels.

8. A method according to claim 7 wherein increasing the threshold levels of the SC threshold profile comprises increasing the threshold level of the SC threshold profile to a level substantially equal to or above the corresponding sidelobe estimate at ranges where the original threshold levels are exceeded by the corresponding sidelobe estimate.

9. A method according to claim 2 wherein selectively modifying the SC threshold profile comprises selectively modifying the SC threshold profile for each new azimuthal vector in the radar video stream prior to SC processing of that new azimuthal vector.

11. A method according to claim 1 wherein the radar signal processing system applies SC processing in the form of Sensitivity Time Control (STC) processing to the radar video stream based on an STC threshold profile.

12. A method according to claim 1 wherein the radar signal processing system applies SC processing in the form of Sensitivity Frequency Control (SFC) processing to the radar video stream based on an SFC threshold profile.

13. A method according to claim 2 wherein each azimuthal vector in the stream of azimuthal vector data is SC processed one by one.

14. A method according to claim 4 wherein the buffer of the radar video stream for each azimuthal vector comprises azimuthal vectors within an azimuthal buffer range centered about the azimthual vector such that each buffer represents a sector of the scanner sweep centered about the current azimuthal vector in the radar video stream being processed.

15. A method according to claim 14 wherein the azimuthal buffer range for each buffer is selected to be substantially equivalent to the azimuthal range of the antenna beam pattern response model.

16. A method according to claim 15 wherein the beam pattern response model represents the antenna response level across the azimuthal buffer range, with the response levels being centered about the main beam.

17. A method according to claim 6 wherein generating each individual candidate sidelobe level from an azimuthal vector in the azimuthal buffer range comprises multiplying the range sample of the azimuthal vector to the corresponding azimuthal response level of the antenna beam pattern response model to generate the individual candidate sidelobe level.

18. A method according to claim 7 wherein the method comprises modifying the SC threshold profile when at least one or more sidelobe estimates exceed their corresponding threshold levels of the SC threshold profile at respective ranges.

19. A method according to claim 1 wherein the SC threshold profile comprises an echo return intensity threshold level for each range sample.

20. A method according to claim 1 further comprising determining the peak echo return intensity level (herein:

peak return level) at each range based on a radar video stream representing a full 360 degree scanner sweep from the radar antenna scanner, and further selectively modifying the SC threshold profile based on the determined peak return level from the full 360 degree scanner sweep.

21. A method according to claim 9 further comprising restoring the original SC threshold profile after each azimuthal vector has been SC processed or prior to each step of selectively modifying the SC threshold profile.

10. A sidelobe clutter suppression system for a radar signal processing system that receives a radar video stream from a radar antenna scanner and applies Sensitivity Control (SC) processing to the radar video stream based on an SC threshold profile that defines an echo intensity threshold over range, the system comprising:

a processor; and

memory associated with the processor; and

wherein the processor is configured to;

receive the radar video stream from the radar antenna scanner;

generate estimates of the sidelobe clutter contribution levels (herein;

sidelobe estimates) based on a buffer of the radar video stream and an antenna beam pattern response model of the radar antenna stored in memory, the stored antenna beam pattern response model representing the radar antenna response level across an azimuthal range centered about a main beam of the radar antenna;

selectively modify the SC threshold profile based on the generated sidelobe estimates to selectively reduce the sensitivity of the SC processing based on the generated sidelobe estimates; and

apply SC processing to the radar video stream based on the selectively modified SC threshold profile to generate an SC processed radar video stream having reduced sidelobe clutter.

22. The sidelobe clutter suppression system according to claim 10, wherein the radar video stream represents the echo return intensities detected by the radar antenna scanner during 360 degree scanner sweeps, sampled in azimuth and range, and wherein the radar video stream comprises a stream of azimuthal vector data, each azimuthal vector representing the echo return intensities at a number of range samples for an azimuthal direction in the radar antenna scanner sweep.

23. The sidelobe clutter suppression system according to claim 22, wherein the processor is configured apply SC processing to each azimuthal vector in the stream of azimuthal vector data one by one.

24. The sidelobe clutter suppression system according to claim 22, wherein the processor is configured to generate sidelobe estimates by determining sidelobe estimates for each new azimuthal vector in the radar video stream such that each azimuthal vector has corresponding sidelobe estimates, and wherein determining sidelobe estimates for each azimuthal vector comprises determining the sidelobe estimates based on a buffer of the radar video stream centered about the azimuthal vector.

25. The sidelobe clutter suppression system according to claim 24, wherein the processor is configured to determine the sidelobe estimates for each azimuthal vector by generating a sidelobe contribution vector representing the sidelobe estimates for the azimuthal vector, the sidelobe contribution vector comprising estimates of the maximum sidelobe contribution levels at each range sample calculated based on the buffer of the radar video stream and the antenna beam pattern response model.

26. The sidelobe clutter suppression system according to claim 25, wherein the processor is configured to determine the sidelobe estimates for each azimuthal vector by generating a set of individual candidate sidelobe levels for each range by applying the antenna beam pattern response model to the cross-range samples from each azimuthal vector within the azimuthal buffer range, and generating the sidelobe contribution vector by selecting at each range sample the maximum of the calculated set of individual candidate sidelobe levels for the range.

27. The sidelobe clutter suppression system according to claim 26, wherein the processor is configured to generate each individual candidate sidelobe level from an azimuthal vector in the azimuthal buffer range by multiplying the range sample of the azimuthal vector to the corresponding azimuthal response level of the antenna beam pattern response model to generate the individual candidate sidelobe level, and wherein the processor is configured to modify the SC threshold profile when at least one or more sidelobe estimates exceed their corresponding threshold levels of the SC threshold profile at respective ranges.

28. The sidelobe clutter suppression system according to claim 24, wherein the buffer of the radar video stream for each azimuthal vector comprises azimuthal vectors within an azimuthal buffer range centered about the azimthual vector such that each buffer represents a sector of the scanner sweep centered about the current azimuthal vector in the radar video stream being processed.

29. The sidelobe clutter suppression system according to claim 28, wherein the azimuthal buffer range for each buffer is selected to be substantially equivalent to the azimthual range of the antenna beam pattern response model, and wherein the beam pattern response model represents the antenna response level across the azimthual buffer range, with the response levels being centered about the main beam.

30. The sidelobe clutter suppression system according to claim 10, wherein the SC threshold profile comprises an echo return intensity threshold level for each range sample, and wherein the processor is configured to selectively modify the SC threshold profile by increasing the threshold levels of the SC threshold profile in range regions where the determined sidelobe estimates exceed the original threshold levels, and wherein increasing the threshold levels of the SC threshold profile comprises increasing the threshold level of the SC threshold profile to a level substantially equal to or above the corresponding sidelobe estimate at ranges where the original threshold levels are exceeded by the corresponding sidelobe estimate.

31. The sidelobe clutter suppression system according to claim 22, wherein the processor is configured to selectively modify the SC threshold profile for each new azimuthal vector in the radar video stream prior to SC processing of that new azimuthal vector, and wherein the processor is further configured to restore the original SC threshold profile after each azimuthal vector has been SC processed or prior to each step of selectively modifying the SC threshold profile.

32. The sidelobe clutter suppression system according to claim 10, wherein the processor is configured to apply either SC processing in the form of Sensitivity Time Control (STC) processing to the radar video stream based on an STC threshold profile or SC processing in the form of Sensitivity Frequency Control (SFC) processing to the radar video stream based on an SFC threshold profile.

33. The sidelobe clutter suppression system according to claim 10, wherein the processor is further configured to determine the peak echo return intensity level (herein:

peak return level) at each range based on a radar video stream representing a full 360 degree scanner sweep from the radar antenna scanner, and further selectively modify the SC threshold profile based on the determined peak return level from the full 360 degree scanner sweep.