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

• US 6,661,366 B2
• Filed: 06/15/2001
• Issued: 12/09/2003
• Est. Priority Date: 06/15/2001
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Yu, Kai-Bor
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/882,348
• Publication Number:
  US 20030020646A1
• Time in Patent Office: 907 Days
• Field of Search: 342/13-20, 342/73-81, 342/89, 342/149-154, 342/159-164, 342/175, 342/195, 342/378-384, 342/147, 342/148
• 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 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.

Claims

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

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

digitally beamforming sub-array data from the plurality of sub-arrays and generating quadrant sub-array beams, each with a respective sub-array beam pattern for each of said plurality of sub-arrays, and each quadrant sub-array beam having nulls at identical null positions, said sub-array beams formed having a constraint of maintaining a given boresight gain of each said quadrant sub-array beam;

steering the nulls associated with the quadrant sub-array beams in directions associated with the sources of interference;

determining sum and difference beams from said plurality of sub-array beams for detecting said target of interest;

determining a monopulse ratio based on the sum and difference beams; and

estimating an angle of arrival of the target using the monopulse ratio.

2. A method in accordance with claim 1, wherein difference beams are determined in azimuth and elevation.

3. A method in accordance with claim 1, wherein said step of digitally beamforming sub-array data from the plurality of sub-arrays and generating quadrant sub-array beams comprises adaptively forming said sub-array beam patterns.

4. 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 quadrant sub-array beam to steer a null of each sub-array beam pattern toward an interference source and maintaining a boresight gain of each sub-array beam pattern;

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

5. A radar system for detecting a radar target of interest in the presence of multiple sources 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 quadrant sub-array beamformer for digitally forming quadrant sub-array beams from said plurality of sub-arrays;

wherein each quadrant sub-array beam has a respective beam pattern including nulls at identical null positions, wherein the nulls of each sub-array beam pattern are steered toward the sources of interference;

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

6. A radar system in accordance with claim 5, further comprising:

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

7. A system in accordance with claim 6, wherein difference beams are determined in elevation and azimuth.

8. A system in accordance with claim 5, wherein said sub-array beam patterns are formed having a constraint of maintaining a boresight gain of each sub-array beam.

9. A system in accordance with claim 5, wherein said sub-array beamformer is an adaptive sub-array beamformer for adaptively forming said sub-array beams.

10. A system in accordance with claim 9, wherein said plurality of sub-arrays comprises four sub-arrays each sub-array formed from a different quadrant of said antenna array.

11. A system in accordance with claim 10, wherein each sub-array beam pattern is formed in accordance with the following equations:

$\begin{array}{c}{\hat{Q}}_1<br><br>\left(T_x,T_y\right)=\hat{Q}<br><br>\left(T_x,T_y\right)<br><br>{\mathrm{<br><br>}}^{\frac{\mathrm{j2\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(T_x<br><br>D_x+T_y<br><br>D_y\right)},\\ {\hat{Q}}_2<br><br>\left(T_x,T_y\right)=\hat{Q}<br><br>\left(T_x,T_y\right)<br><br>{\mathrm{<br><br>}}^{\frac{\mathrm{j2\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(-T_x<br><br>D_x+T_y<br><br>D_y\right)},\\ {\hat{Q}}_3<br><br>\left(T_x,T_y\right)=\hat{Q}<br><br>\left(T_x,T_y\right)<br><br>{\mathrm{<br><br>}}^{\frac{\mathrm{j2\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(-T_x<br><br>D_x-T_y<br><br>D_y\right)},\\ {\hat{Q}}_4<br><br>\left(T_x,T_y\right)=\hat{Q}<br><br>\left(T_x,T_y\right)<br><br>{\mathrm{<br><br>}}^{\frac{\mathrm{j2\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>\left(T_x<br><br>D_x-T_y<br><br>D_y\right)},\end{array}$

wherein,

D_x is a distance in azimuth between a center of a respective sub-array and a center of said antenna array;

D_y is a distance in elevation between a center of a respective sub-array and said center of said antenna array;

λ

is a wavelength of transmitted radar energy;

T_x is a directional cosine representing azimuth with respect to said center of said antenna array;

T_y is a directional cosine representing elevation with respect to said center of said antenna array;

{circumflex over (Q)}₁(T_x,T_y) is an estimated first quadrant beam located at (D_x, D_y) with respect to said center of said antenna array;

{circumflex over (Q)}₂(T_x,T_y) is an estimated second quadrant beam located at (−

D_x, D_y) with respect to said center of said antenna array;

{circumflex over (Q)}₃(T_x,T_y) is an estimated third quadrant beam located at (−

D_x, −

D_y) with respect to said center of said antenna array;

{circumflex over (Q)}₄(T_x,T_y) is an estimated fourth quadrant beam located at (D_x, −

D_y) with respect to said center of said antenna array; and

{circumflex over (Q)}(T_x,T_y) is an estimated common sub-array factor located at said center of said antenna array.

12. A system in accordance with claim 11, wherein a calculation of monopulse ratios results in the following equations:

${\hat{m}}_A=j<br><br>\text{\hspace{1em}<br><br>}<br><br>\tan <br><br>\left(\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>T_x<br><br>D_x\right),<br><br>{\hat{m}}_E=j<br><br>\text{\hspace{1em}<br><br>}<br><br>\tan <br><br>\left(\frac{2<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}<br><br>T_y<br><br>D_y\right),$

wherein,

{circumflex over (m)}_A is an estimated monopulse ratio in azimuth; and

{circumflex over (m)}_E is an estimated monopulse ratio in elevation.

13. A computer readable medium having embodied thereon a computer program for detecting a radar target of interest in the presence of multiple sources of 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 quadrant sub-array beam for each of said plurality of sub-arrays, wherein at least one null of each sub-array beam is steered toward a respective one of the sources of 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 beams; 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.

14. A computer readable medium in accordance with claim 13, further comprising means for maintaining an estimated angle of arrival of said target of interest, said means for maintaining comprising:

means for updating each quadrant sub-array beam to steer a null of each sub-array beam pattern toward an interference source 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 beams; 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.

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

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

digitally beamforming sub-array data from the plurality of sub-arrays and adaptively generating four quadrant sub-array beams for each of the plurality of sub-arrays using all of the sub-array data elements, each quadrant sub-array beam having a respective sub-array beam pattern and each quadrant sub-array beam having identical nulls and constrained with a given boresight gain;

steering the nulls associated with the quadrant sub-array beams in directions associated with each of the sources of interference;

determining sum and difference beams from said plurality of sub-array beams for detecting said target of interest;

determining a monopulse ratio based on the sum and difference beams; and

estimating an angle of arrival of the target using the monopulse ratio.