Radar clutter suppression system

• US 9,213,089 B2
• Filed: 02/09/2015
• 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: Phillips, Roger, Mowbray, Robert Stephen
• Primary Examiner(s): BYTHROW, PETER M
• Application Number:
  US14/617,326
• Publication Number:
  US 20150153446A1
• Time in Patent Office: 309 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:

receiving the radar video stream from the radar antenna scanner;

determining the peak echo return intensity level (herein;

peak return level) at each range based on radar video stream representing a full scanner sweep stored in memory of the radar signal processing system;

selectively modifying the SC threshold profile based on the determined peak echo return intensity levels from the full scanner sweep and an antenna sidelobe margin factor that is based on the antenna characteristics of the radar antenna scanner to thereby selectively reduce the sensitivity of the SC processing based on the determined peak echo return intensity levels and the antenna sidelobe margin factor; 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 its 360 degree 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 each azimuthal vector in the stream of azimuthal vector data is SC processed one by one.

4. 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.

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

6. A method according to claim 2 wherein determining the peak return level at each range comprises determining the peak return level for each range based on the maximum echo return intensity from all or a sample of azimuthal vectors in a full 360 degree sweep of the radar antenna scanner.

7. A method according to claim 2 wherein determining the peak return level at each range comprises, for each azimuthal vector, generating a peak return level vector comprising the peak return levels at each range sample based on a buffer of the radar video stream comprising azimuthal vectors within an azimuthal buffer range relative to the azimuthal vector being SC processed, and selectively modifying the SC threshold profile comprises, for each azimuthal vector, selectively modifying the SC threshold profile based on the generated peak return level vector for the azimuthal vector prior to SC processing of the azimuthal vector.

8. A method according to claim 7 wherein the buffer of the radar video stream comprises azimuthal vectors within an azimuthal buffer range of 360 degrees centered about the azimuthal vector being SC processed.

9. A method according to claim 7 wherein the buffer of the radar video stream comprises azimuthal vectors within an azimuthal buffer range of 360 degrees occurring before the azimuthal vector being SC processed.

10. A method according to claim 2 wherein determining the peak return level at each range comprises generating a peak return level vector once for each full sweep, the peak return level vector comprising the peak return levels at each range based on a buffer of the radar video stream comprising azimuthal vectors within an azimuthal buffer range relative to the sweep, and selectively modifying the SC threshold profile comprises selectively modifying the SC profile once for each full sweep based on the generated peak return level vector for that sweep prior to SC processing of the radar video stream of the sweep.

11. A method according to claim 10 wherein the buffer of the radar video stream comprises azimuthal vectors within an azimuthal buffer range of 360 degrees preceding the sweep being SC processed.

12. A method according to claim 2 wherein each sweep of radar video stream is segmented, and determining the peak return level at each range comprises generating a peak return level vector once for each segment of the sweep, the peak return level vector comprising the peak return levels at each range based on a buffer of the radar video stream comprising azimuthal vectors within an azimuthal buffer range relative to the sweep, and selectively modifying the SC threshold profile comprises selectively modifying the SC profile once for each segment based on the generated peak return level vector for that segment prior to SC processing of the radar video stream of the segment.

13. A method according to claim 12 wherein the buffer of the radar video stream comprises azimuthal vectors within an azimuthal buffer range of 360 degrees preceding the segment being SC processed.

14. A method according to claim 1 further comprising modifying the determined peak return levels based on the antenna sidelobe margin factor to generate modified peak return levels and selectively modifying the SC threshold profile comprises selectively modifying the SC threshold profile based on the modified peak return levels.

15. A method according to claim 14 comprising selecting the antenna sidelobe margin factor based on the antenna beam pattern response of the radar antenna scanner.

16. A method according to claim 14 wherein the SC threshold profile comprises an echo return intensity threshold level for each range sample, and wherein selectively modifying the SC threshold profile comprises increasing the threshold levels of the SC threshold profile in range regions where the modified peak return levels exceeds the original threshold levels.

17. A method according to claim 16 wherein increasing the threshold levels of the SC threshold profile comprises increasing the threshold level of the SC threshold profile to a level subsequently equal to or above the corresponding modified peak return level at-ranges where the original threshold levels are exceeded by their corresponding modified peak return level.

18. A method according to claim 16 wherein the method comprises modifying the SC threshold profile when at least one or more of the modified peak return levels exceed their corresponding threshold levels of the SC threshold profile at respective ranges.

19. 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.

20. A method according to claim 19 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.

21. A method according to claim 1 further comprising 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, and further selectively modifying the SC threshold profile based on the determined estimates of the sidelobe clutter contribution levels.

22. 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;

determine the peak echo return intensity level (herein;

peak return level) at each range based on radar video stream representing a full scanner sweep stored in memory;

selectively modify the SC threshold profile based on the determined peak echo return intensity levels from the full scanner sweep and an antenna sidelobe margin factor that is based on the antenna characteristics of the radar antenna scanner to thereby selectively reduce the sensitivity of the SC processing based on the determined peak echo return intensity levels and the antenna sidelobe margin factor; 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.

23. A radar signal processing system according to claim 22 wherein the radar video stream represents the echo return intensities detected by the radar antenna scanner during its 360 degree 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.

24. A radar signal processing system according to claim 23 wherein the processor is configured to apply SC processing to each azimuthal vector in the stream of azimuthal vector data one by one.

25. A radar signal processing system according to claim 22 wherein the processor is configured to apply 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) based on an SFC threshold profile.

26. A radar signal processing system according to claim 23 wherein the processor is configured to determine the peak return level at each range by determining the peak return level for each range based on the maximum echo return intensity from all or a sample of azimuthal vectors in a full 360 degree sweep of the radar antenna scanner.

27. A radar signal processing system according to claim 23 wherein the processor is configured to determine the peak return level at each range by, for each azimuthal vector, generating a peak return level vector comprising the peak return levels at each range sample based on a buffer of the radar video stream comprising azimuthal vectors within an azimuthal buffer range relative to the azimuthal vector being SC processed, and wherein the processor is configured to selectively modify the SC threshold profile by, for each azimuthal vector, selectively modifying the SC threshold profile based on the generated peak return level vector for the azimuthal vector prior to SC processing of the azimuthal vector.

28. A radar signal processing system according claim 27 wherein the buffer of the radar video stream comprises azimuthal vectors within an azimuthal buffer range of 360 degrees centered about or occurring before the azimuthal vector being SC processed.

29. A radar signal processing system according claim 23 wherein the processor is configured to determine the peak return level at each range by generating a peak return level vector once for each full sweep, the peak return level vector comprising the peak return levels at each range based on a buffer of the radar video stream comprising azimuthal vectors within an azimuthal buffer range of 360 degrees preceding the sweep being SC processed, and wherein the processor is configured to selectively modify the SC threshold profile by selectively modifying the SC profile once for each full sweep based on the generated peak return level vector for that sweep prior to SC processing of the radar video stream of the sweep.

30. A radar signal processing system according claim 23 wherein each sweep of radar video stream is segmented, and the processor is configured to determine the peak return level at each range by generating a peak return level vector once for each segment of the sweep, the peak return level vector comprising the peak return levels at each range based on a buffer of the radar video stream comprising azimuthal vectors within an azimuthal buffer range of 360 degrees preceding the segment being SC processed, and wherein the processor is configured to selectively modify the SC threshold profile by selectively modifying the SC profile once for each segment based on the generated peak return level vector for that segment prior to SC processing of the radar video stream of the segment.

31. A radar signal processing system according claim 22 wherein the processor is further configured to modify the determined peak return levels based on the antenna sidelobe margin factor to generate modified peak return levels and wherein the processor is configured to selectively modify the SC threshold profile by selectively modifying the SC threshold profile based on the modified peak return levels.

32. A radar signal processing system according claim 31 wherein the processor is configured to select the antenna sidelobe margin factor based on the antenna beam pattern response of the radar antenna scanner.

33. A radar signal processing system according claim 31 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 modified peak return levels exceeds the original threshold levels.

34. A radar signal processing system according claim 33 wherein the processor is configured to increase the threshold levels of the SC threshold profile by increasing the threshold level of the SC threshold profile to a level subsequently equal to or above the corresponding modified peak return level at ranges where the original threshold levels are exceeded by their corresponding peak return level.

35. A radar signal processing system according claim 33 wherein the processor is configured to modify the SC threshold profile when at least one or more of the modified peak return levels exceed their corresponding threshold levels of the SC threshold profile at respective ranges.

36. A radar signal processing system according claim 23 wherein the processor is configured to selectively modify the SC threshold profile by 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 and then 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.

37. A radar signal processing system according claim 22 wherein the processor is further configured to determine 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, and wherein the processor is configured to further selectively modify the SC threshold profile based on the determined estimates of the sidelobe clutter contribution levels.