Adaptive digital sub-array beamforming and deterministic sum and difference beamforming, with jamming cancellation and monopulse ratio preservation

• US 20030020646A1
• Filed: 06/15/2001
• Published: 01/30/2003
• Est. Priority Date: 06/15/2001
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Yu, Kai-Bor
• Granted Patent: US 6,661,366 B2
• Time in Patent Office: Days
• US Class Current: 342/17
• CPC Class Codes: G01S 13/4409 HF sub-systems particularly adapted therefor, e.g. circuits for signal combination multi-lobing aerials or aerial systems H01Q25/00
• CPC Class Codes: G01S 13/4463 using phased arrays
• CPC Class Codes: H01Q 25/02 providing sum and difference patterns H01Q25/04 takes precedence
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling

Abstract

A radar system and technique provide the capability to detect a target of interest and maintain the detection in the presence of multiple mainlobe and sidelobe jamming interference. The system and technique utilize the versatility of digital beamforming to form sub-arrays for canceling jamming interference. Jamming is adaptively suppressed in the sub-arrays prior to using conventional deterministic methods to form the sum, Σ, and difference, Δ, beams for monopulse processing. The system and technique provide the ability to detect a target of interest, provide an undistorted monopulse ratio, m, and maintain target angle estimation, in the presence of multiple mainlobe and multiple sidelobe jammers. Further, this system and technique are not constrained by requiring a priori knowledge of the jamming interference.

Claims

1. A method for detecting a radar target of interest in the presence of radar jamming interference, said method comprising the steps of:

forming a plurality of sub-arrays from an antenna array;

forming a respective sub-array beam pattern for each of said plurality of sub-arrays;

wherein at least one null of each sub-array beam pattern is steered toward an interference; and

determining a sum beam from said sub-array beam patterns for detecting said target of interest.

2. A method in accordance with claim 1, further comprising the steps of:

determining at least one difference beam from said sub-array beam patterns; and

determining at least one monopulse ratio from said sum and at least one difference beams for estimating an angle of arrival of said target of interest.

3. A method in accordance with claim 2, wherein difference beams are determined in azimuth and elevation.

4. A method in accordance with claim 1, wherein said sub-array beam patterns are formed having a constraint of maintaining a boresight gain of each sub-array beam pattern.

5. A method in accordance with claim 1, wherein said step of forming said sub-array beam patterns comprises adaptively forming said sub-array beam patterns.

6. A method in accordance with claim 1, wherein said step of forming said sub-array beam patterns comprises digitally beamforming said sub-array beam patterns.

7. A method in accordance with claim 1 further comprising the step of maintaining an estimated angle of arrival of said target of interest, said step of maintaining comprising:

updating each sub-array beam pattern to steer said at least one null of each sub-array beam pattern toward interference and to maintain a boresight gain of each sub-array beam pattern;

determining updated sum and difference beams from said updated sub-array beam patterns; and

determining at least one updated monopulse ratio from said updated sum and difference beams for maintaining an estimated angle of arrival of said target of interest.

8. A radar system for detecting a radar target of interest in the presence of interference, said system comprising:

an antenna array for providing antenna array element data;

a summer for forming a plurality of sub-arrays from said antenna array element data;

a sub-array beamformer for forming a respective sub-array beam pattern from each of said plurality of sub-arrays;

wherein at least one null of each sub-array beam pattern is steered toward an interference;

a monopulse summer for forming sum beams from said sub-array beam patterns for detecting said target of interest.

9. A radar system in accordance with claim 8, further comprising:

a monopulse difference beamformer for forming at least one difference beam from said sub-array beam patterns; and

a monopulse ratio former for determining at least one monopulse ratio from said sum and at least one difference beams for estimating an angle of arrival of said target of interest.

10. A system in accordance with claim 9, wherein difference beams are determined in elevation and azimuth.

11. A system in accordance with claim 8, wherein said sub-array beamformer is a digital beamformer.

12. A system in accordance with claim 8, wherein said sub-array beam patterns are formed having a constraint of maintaining a boresight gain of each sub-array beam pattern.

13. A system in accordance with claim 8, wherein said sub-array beamformer is an adaptive sub-array beamformer for adaptively forming said sub-array beam patterns.

14. A system in accordance with claim 13, wherein said plurality of sub-arrays comprises four sub-arrays each sub-array formed from a different quadrant of said antenna array.

15. A system in accordance with claim 14, wherein each sub-array beam pattern is formed in accordance with the following equations:

16. A system in accordance with claim 15, wherein a calculation of monopulse ratios results in the following equations:

17. A computer readable medium having embodied thereon a computer program for detecting a radar target of interest in the presence of a interference, the computer readable program comprising:

means for causing a processor to form a plurality of sub-arrays from an antenna array;

means for causing said processor to adaptively form a respective sub-array beam pattern for each of said plurality of sub-arrays, wherein at least one null of each sub-array beam pattern is steered toward an interference and a boresight gain of each sub-array beam pattern is maintained;

means for causing said processor to determine sum and difference beams from said sub-array beam patterns; and

means for causing said processor to determine at least one monopulse ratio from said sum and difference beams for detecting a radar target of interest and for estimating an angle of arrival of said target of interest.

18. A computer readable medium in accordance with claim 17, further comprising means for maintaining an estimated angle of arrival of said target of interest, said means for maintaining comprising:

means for updating each sub-array beam pattern to steer said at least one null of each sub-array beam pattern toward interference and to maintain a boresight gain of each sub-array beam pattern;

means for determining updated sum and difference beam patterns from said updated sub-array beam patterns; and

means for determining at least one updated monopulse ratio from said updated sum and difference beams for maintaining an estimated angle of arrival of said target of interest.