Multiplatform GMTI radar with enhanced SNR, monopulse

• US 9,285,469 B1
• Filed: 10/29/2014
• Issued: 03/15/2016
• Est. Priority Date: 10/29/2014
• Status: Active Grant

• Current Assignee: SRC, Inc.
• Original Assignee: SRC, Inc.
• Inventors: Schuman, Harvey K., Thomas, Daniel D. Jr.
• Primary Examiner(s): Sotomayor, John B
• Assistant Examiner(s): Windrich, Marcus
• Application Number:
  US14/526,775
• Time in Patent Office: 503 Days
• Field of Search: 342/17, 342/59, 342/80, 342/160, 342/161
• US Class Current: 1/1
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 13/4418 with means for eliminating radar-dependent errors in angle measurements, e.g. multipath effects
• CPC Class Codes: G01S 13/4427 with means for eliminating the target-dependent errors in angle measurements, e.g. glint, scintillation effects
• CPC Class Codes: G01S 13/4454 phase comparisons monopulse, i.e. comparing the echo signals received by an interferometric antenna arrangement
• CPC Class Codes: G01S 13/4472 with means specially adapted to airborne monopulse systems clutter elimination using Doppler effect: G01S13/449
• CPC Class Codes: G01S 13/449 Combined with MTI or Doppler processing circuits
• 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
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00

Abstract

The present invention is directed to a ground moving target (GMTI) radar that can detect targets, including dismounts, with very small minimum detectable velocities by combining signals from antennas on different spatially separated platforms in a main beam clutter-suppressing spatially adaptive process without requiring that the relative positions of the antenna phase centers be accurately tracked. The clutter nulling is in addition to that provided by the Doppler filters. The spatial displacement provides a narrow mainbeam clutter null reducing undesired target suppression. The clutter-suppressing spatially adaptive structure is used in both the sum and delta channels of the monopulse processor so that the beam distortion caused by the spatial nulling is compensated for, and the monopulse look-up process is preserved to maintain angle accuracy. Noncoherent integration is employed to recover signal to noise loss resulting from the uncertain relative locations of the platforms.

Claims

1. A GMTI radar system comprising:

a signal input portion configured to receive first main channel radar return signals and second main channel radar return signals from a first main radar receiver and a second main radar receiver, respectively, both being disposed on a main airborne platform, the data input portion also configured to receive first auxiliary channel radar return signals and second auxiliary channel radar return signals from at least one first auxiliary radar receiver and at least one second auxiliary radar receiver, respectively, both being disposed on at least one auxiliary airborne platform, the main airborne platform being independent and spatially separated from the auxiliary airborne platform;

a plurality of Doppler filters coupled to the signal input portion, the plurality of Doppler filters being configured to derive;

a first main clutter signal and a first main target signal from the first main channel radar return signals;

at least one first auxiliary clutter signal and at least one first auxiliary target signal from the first auxiliary channel radar return signals;

a second main clutter signal and a second main target signal from the second main channel radar return signals; and

at least one second auxiliary clutter signal and at least one second auxiliary target signal from the second auxiliary channel radar return signals;

a first adaptive cancelation circuit coupled to the plurality of Doppler filters, the first adaptive cancelation circuit being configured to generate a first weight vector that is a function of the first main clutter signal and the at least one first auxiliary clutter signal and apply the first weight vector to the at least one first auxiliary target signal to obtain a first weighted auxiliary target signal, the first adaptive cancelation circuit being further configured to combine the first weighted auxiliary target signal and the first main target signal to provide a first clutter suppressed target signal;

a second adaptive cancelation circuit coupled to the plurality of filters, the second adaptive cancelation circuit being configured to generate a second weight vector that is a function of the second main clutter signal and the at least one second auxiliary clutter signal and apply the second weight vector to the at least one second auxiliary target signal to obtain a second weighted auxiliary target signal, the second adaptive cancelation circuit being further configured to combine the second weighted auxiliary target signal and the second main target signal to provide a second clutter suppressed target signal; and

a monopulse angle estimation circuit coupled to the first adaptive processing circuit and the second adaptive processing circuit, the monopulse angle estimation circuit being configured to provide a monopulse angle estimation ratio that is a function of the first clutter suppressed target signal and the second clutter suppressed target signal, but not a function of the first weight vector or the second weight vector.

2. The system of claim 1, further comprising a target detector configured to non-coherently integrate the first clutter suppressed target signals from successive coherent processing intervals (CPIs) to obtain a detection estimate.

3. The system of claim 2, wherein the detection estimate is characterized by an improved signal to noise ratio (SNR) relative to the first clutter suppressed target signal and the second clutter suppressed target signal.

4. The system of claim 2, wherein the target detector is configured to detect a target from the detection estimate when the detection estimate is greater than or equal to a predetermined threshold.

5. The system of claim 1, wherein the plurality of Doppler filters includes a plurality of first Doppler filters disposed in parallel to a plurality of first auxiliary Doppler filters and a plurality of second Doppler filters disposed in parallel to a plurality of second auxiliary Doppler filters, and wherein the plurality of first Doppler filters are configured to provide the first main clutter signal and the first main target signal, the plurality of first auxiliary Doppler filters are configured to provide the at least one first auxiliary clutter signal and the at least one first auxiliary target signal, the plurality of second Doppler filters are configured to provide the second main clutter signal and the second main target signal, and the plurality of second auxiliary Doppler filters are configured to provide the at least one second auxiliary clutter signal and the at least one second auxiliary target signal.

6. The system of claim 5, wherein each of the first main clutter signal, the first main target signal, the at least one first auxiliary clutter signal, the at least one first auxiliary target signal, the second main clutter signal, the second main target signal, the at least one second auxiliary clutter signal, and the at least one second auxiliary target signal are characterized by a predetermined Doppler frequency and a predetermined range bin.

7. The system of claim 5, wherein the at least one first main target signal includes a plurality of first main target signals provided by the plurality of first Doppler filters and the at least one first auxiliary clutter signal includes a plurality of first auxiliary clutter signals provided by the plurality of first auxiliary Doppler filters, the plurality of first auxiliary Doppler filters includes a first bank of first auxiliary filters coupled to the signal input portion and at least one second bank of first auxiliary filters disposed in parallel to the first bank of first auxiliary filters, the at least one second bank of first auxiliary filters being coupled to the signal input portion by way of a first fast time delay tap.

8. The system of claim 7, wherein each of the plurality of first auxiliary Doppler filters corresponds to a predetermined Doppler frequency and a predetermined range bin, the predetermined range bin being characterized by a radar return delay time, the time delay of the first fast time delay tap being a fraction of a range bin duration.

9. The system of claim 7, wherein the first weight vector is given by:

w=−

R₂₂<sup>−

1</sup>R₁₂, wherein R₂₂ denotes a covariance matrix estimate based on the plurality of first auxiliary clutter signals and R₁₂ denotes a covariance vector estimate based on the plurality of first main target signals and the plurality of first auxiliary clutter signals.

10. The system of claim 5, wherein the at least one second main target signal includes a plurality of second main target signals provided by the plurality of second Doppler filters and the at least one second auxiliary clutter signal includes a plurality of second auxiliary clutter signals provided by the plurality of second auxiliary Doppler filters, the plurality of second auxiliary Doppler filters includes a first bank of second auxiliary filters coupled to the signal input portion and at least one second bank of second auxiliary filters disposed in parallel to the first bank of second auxiliary filters, the at least one second bank of second auxiliary filters being coupled to the signal input portion by way of a fast time delay tap.

11. The system of claim 10, wherein each of the plurality of second auxiliary Doppler filters corresponds to a predetermined Doppler frequency and a predetermined range bin, the predetermined range bin being characterized by a radar return delay time, the time delay of the second fast time delay tap being a fraction of a range bin duration.

12. The system of claim 10, wherein the second weight vector is given by:

w=−

R₂₂<sup>−

1</sup>R₁₂, wherein R₂₂ denotes a covariance matrix estimate based on the plurality of second auxiliary clutter signals and R₁₂ denotes a covariance vector estimate based on the plurality of second main target signals and the plurality of second auxiliary clutter signals.

13. The system of claim 1, wherein the first adaptive cancelation circuit further comprises:

a first weight determination circuit configured to generate a first weight vector that is a function of the first main clutter signal and the at least one first auxiliary clutter signal;

a first weight application circuit configured to apply the first weight vector to the at least one first auxiliary target signal to obtain a weighted first auxiliary target signal; and

a first clutter cancelation circuit configured to subtract the weighted first auxiliary target signal from the first main target signal to provide the first clutter suppressed target signal.

14. The system of claim 13, wherein the second adaptive cancelation circuit further comprises:

a second weight determination circuit configured to generate a second weight vector that is a function of the second main clutter signal and the at least one second auxiliary clutter signal;

a second weight application circuit configured to apply the second weight vector to the at least one second auxiliary target signal to obtain a weighted second auxiliary target signal; and

a second clutter cancelation circuit configured to subtract the weighted second auxiliary target signal from the second main target signal to provide the second clutter suppressed target signal.

15. The system of claim 14, wherein the first weight determination circuit and the second weight determination circuit each include a range selection circuit configured to determine a size of a cell-under-test (CUT) based on a measure of the homogeneity of the at least one first auxiliary clutter signal and the at least one second auxiliary clutter signal, respectively, and wherein each CUT is centered on a predetermined range bin.

16. The system of claim 15, wherein the size of the cell-under-test is based on clutter signals from a relatively large number of adjacent range bins when the clutter signals are relatively homogeneous, and wherein the size of the cell-under-test is based on clutter signals from one range bin or a relatively small number of adjacent range bins when the clutter signals are not homogeneous.

17. The system of claim 14, wherein the first weight application circuit and the second weight application circuit apply the first weight vector and the second weight vector to the at least one first auxiliary target signal and the at least one second auxiliary target signal, respectively, using a sliding window operation.

18. The system of claim 17, wherein the sliding window is incremented by generating a new first weight vector and a new second weight vector for each CUT.

19. The system of claim 1, wherein the first weight vector and the second weight vector are given by:

w=−

R₂₂<sup>−

1</sup>R₁₂, wherein R₂₂ denotes a covariance matrix estimate based on a plurality of auxiliary clutter signals and R₁₂ denotes a covariance vector estimate based on a plurality of main target signals and the plurality of auxiliary clutter signals.

20. The system of claim 1, wherein the monopulse angle estimation ratio) is given by:

21. A GMTI radar system comprising:

a non-adaptive signal processing circuit configured to provide a first main clutter signal and a first main target signal from a plurality of first main channel radar return signals obtained from a first main radar receiver and provide a second main clutter signal and a second main target signal from a plurality of second main channel radar return signals obtained from a second main radar receiver, the first main radar receiver and the second main radar receiver being disposed on a first movable platform, the non-adaptive signal processing circuit being further configured to provide at least one first auxiliary clutter signal and at least one first auxiliary target signal from a plurality of first auxiliary channel radar return signals obtained from at least one first auxiliary radar receiver and provide at least one second auxiliary clutter signal and at least one second auxiliary target signal from a plurality of second auxiliary channel radar return signals obtained from at least one second auxiliary radar receiver, the at least one first auxiliary radar receiver and the at least one second auxiliary radar receiver being disposed on at least one auxiliary movable platform, the main movable platform being independent and spatially separated from the auxiliary movable platform;

an adaptive signal processing circuit configured combine a first weighted auxiliary target signal and the first main target signal to provide a first clutter suppressed target signal and combine a second weighted auxiliary target signal and the second main target signal to provide a second clutter suppressed target signal, the first weighted auxiliary target signal and the second weighted auxiliary target signal being a function of a first adaptive weight vector and a second adaptive weight vector, respectively; and

a monopulse angle estimation circuit coupled to the adaptive signal processing circuit, the monopulse angle estimation circuit being configured to provide a monopulse angle estimation ratio that is a function of the first clutter suppressed target signal and the second clutter suppressed target signal, but not a function of the first weight vector or the second weight vector.

22. The system of claim 21, wherein the non-adaptive signal processing circuit includes a signal input portion configured to receive the plurality of first main channel radar return signals and the plurality of second main channel radar return signals from the first main radar receiver and the second main radar receiver, respectively, the data input portion also being configured to receive the plurality of first auxiliary channel radar return signals and the plurality of second auxiliary channel radar return signals from the at least one first auxiliary radar receiver and the at least one second auxiliary radar receiver, respectively.

23. The system of claim 22, wherein the non-adaptive signal processing circuit includes a plurality of Doppler filters coupled to the signal input portion, the plurality of Doppler filters being configured to:

filter the first main channel radar return signals to obtain the first main clutter signal and the first main target signal;

filter the first auxiliary channel radar return signals to obtain the at least one first auxiliary clutter signal and at least one first auxiliary target signal;

filter the second main channel radar return signals to obtain the second main clutter signal and the second main target signal from; and

filter the second auxiliary channel radar return signals to obtain the at least one second auxiliary clutter signal and at least one second auxiliary target signal.

24. The system of claim 21, wherein the adaptive signal processing circuit comprises:

a weight determination processing circuit configured to determine the first adaptive weight vector as a function of the first main clutter signal and the at least one first auxiliary clutter signal, the weight determination processing circuit being further configured to determine the second adaptive weight vector as a function of the second main clutter signal and the at least one second auxiliary clutter signal;

a weight application circuit configured to apply the first adaptive weight vector to the at least one first auxiliary target signal to obtain the weighted first auxiliary target signal, the weight application circuit being also configured to apply the second adaptive weight vector to the at least one second auxiliary target signal to obtain a weighted second auxiliary target signal; and

a clutter cancelation circuit configured to subtract the weighted first auxiliary target signal from the first main target signal to obtain the first clutter suppressed target signal, the clutter cancelation circuit being further configured to subtract the weighted second auxiliary target signal from the second main target signal to obtain the second clutter suppressed target signal.

25. The system of claim 24, wherein the weight determination circuit includes a range selection circuit configured to determine a size of a range cell-under-test (CUT) based on a measure of the homogeneity of the at least one first auxiliary clutter signal and the at least one second auxiliary clutter signal, respectively, and wherein each CUT is centered on a predetermined range bin.

26. The system of claim 25, wherein the size of the range cell-under-test is based on clutter signals from a relatively large number of adjacent range bins when the clutter signals are relatively homogeneous, and wherein the size of the cell-under-test is based on clutter signals from one range bin or a relatively small number of adjacent range bins when the clutter signals are not homogeneous.

27. The system of claim 24, wherein the weight application circuit applies the first adaptive weight vector and the second adaptive weight vector to the at least one first auxiliary target signal and the at least one second auxiliary target signal, respectively, using a sliding window operation.

28. The system of claim 27, wherein the sliding window is incremented by generating a new first weight vector and a new second weight vector for each CUT.

29. The system of claim 21, further comprising a target detector configured to non-coherently integrate the first clutter suppressed target signals from successive coherent processing intervals (CPIs) to obtain a detection estimate.

30. The system of claim 29, wherein the detection estimate is characterized by an improved signal to noise ratio (SNR) relative to the first clutter suppressed target signal and the second clutter suppressed target signal.

31. The system of claim 30, wherein the target detector is configured to detect a target from the detection estimate when the detection estimate is greater than or equal to a predetermined threshold.

32. The system of claim 21, wherein the first adaptive weight vector and the second adaptive weight vector are given by:

w=−

R₂₂<sup>−

1</sup>R₁₂, wherein R₂₂ denotes a covariance matrix estimate based on a plurality of auxiliary clutter signals and R₁₂ denotes a covariance vector estimate based on a plurality of main target signals and the plurality of auxiliary clutter signals.

33. The system of claim 21, wherein the monopulse angle estimation ratio) is given by:

34. The system of claim 21, wherein the data input portion, the non-adaptive processing portion and the adaptive processing portion are disposed at a location remote from the first GMTI radar receiver or the at least one auxiliary GMTI radar receiver, and wherein the first coherent radar return samples and the second radar return samples are provided to the data input portion via a data link.

35. The system of claim 21, wherein the GMTI radar system includes a radar transmitter that is configured as a monostatic radar transmitter or as a bistatic radar transmitter.

36. The system of claim 35, wherein the bistatic radar transmitter is disposed aboard a separate and remote airborne or spaceborne platform.

37. The system of claim 21, wherein the auxiliary movable platform includes a plurality of auxiliary movable platforms.

38. The system of claim 21, wherein the main airborne platform and the at least one auxiliary airborne platform are separated by a cross range dimension (Δ

Y) that is substantially within a range of about 5-20 wavelengths (λ

) of a transmitted radar signal, and wherein a lateral separation dimension (Δ

X) and an altitude separation between the main airborne platform and the at least one auxiliary airborne platforms is substantially unconstrained.

39. The system of claim 21, wherein the signal input portion is disposed on either the first platform or the at least one second platform.

40. The system of claim 21, wherein the signal input portion is coupled to the first main radar receiver, the second main radar receiver, the at least one first auxiliary radar receiver or the at least one second auxiliary radar receiver via a data link.

41. The system of claim 21, wherein the main movable platform includes a ground-based platform, an airborne platform or a spaceborne platform.

42. The system of claim 21, wherein the auxiliary movable platform includes a ground-based platform, an airborne platform or a spaceborne platform.