Multi-channel moving target radar detection and imaging apparatus and method

• US 6,400,306 B1
• Filed: 12/17/1999
• Issued: 06/04/2002
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: Accipiter Radar Technologies Inc.
• Original Assignee: Sicom Systems Limited
• Inventors: Nohara, Timothy Joseph, Weber, Peter Thomas
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/466,326
• Time in Patent Office: 900 Days
• Field of Search: 342/25, 342/159-164, 342/175, 342/176, 342/179, 342/189-197, 342/352
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time

Abstract

A radar detection and imaging system provides for the simultaneous imaging of the stationary objects on the earth'"'"'s surface and the detection and imaging of moving targets. The radar system includes at least one transmitting aperture and a plurality of receiving apertures that are simultaneously operated in a synthetic aperture radar (SAR) mode caused by the motion of the satellite or airborne platform on which they are mounted. Each receiving aperture is connected to its own coherent receiver and the digitized signals from all receivers are processed to image both stationary clutter and moving targets. The system employs space-time adaptive processing (STAP) algorithms to better compensate for channel mismatches, better suppress stationary clutter, and to suppress mainbeam jamming. Moving target detection and estimation modules are also included and are their performance is improved as a result of the STAP algorithms. The system also employs SAR processing algorithms to create high-resolution images of stationary objects, and to image moving targets. The SAR and STAP algorithms are uniquely integrated in the radar signal processor (RSP) to provide improved performance while reducing the computational requirements, facilitating real-time implementation.

Claims

1. A radar system comprising:

at least one transmitting antenna connected to a pulsed radio frequency generator;

a plurality of receiving antennas;

a plurality of receivers connected to respective ones of said receiving antennas;

a plurality of signal delays, each of said receivers being operatively connected to at least one of said signal delays to produce a plurality of delayed incoming radar signals in respective pseudochannels;

a plurality of synthetic aperture radar (SAR) modules operatively connected to said receivers and said delays for operating on signals from said receivers and from said signal delays to produce a plurality of SAR-processed signals;

a systems formation module coupled to outputs of said SAR modules for forming or selecting at least one grouping of said SAR-processed signals; and

at least one moving target indication (MTI) module connected to said systems formation module for performing clutter suppression operations on said grouping of said SAR-processed signals.

2. The radar system of claim 1 wherein said SAR modules are coarse SAR processors, further comprising at least one fine SAR processor connected to an output of said MTI module.

3. The radar system of claim 2 wherein each of said first stages are coarse SAR processors that include a subaperture formation module, a range compression module, and a coarse Doppler calculation module.

4. The radar system of claim 3 wherein said second stage is a fine SAR processor that includes a fine azimuth calculation module.

5. The radar system of claim 2, further comprising a stationary imaging computation module connected to at least one of said SAR modules for producing a signal encoding stationary objects, further comprising at least one additional fine SAR processor connected to an output of said stationary imaging computation module.

6. The radar system of claim 5, further comprising a stationary target detection and estimation module for detecting and locating stationary targets, said stationary target detection and estimation module being connected to said additional fine SAR processor.

7. The radar system of claim 2 wherein said fine SAR processor is one of a plurality of fine SAR processors, further comprising a moving target detection module, each of said fine SAR processors being connected to said moving target detection module.

8. The radar system of claim 7, further comprising a moving target estimation module, each of said fine SAR processors and said moving target detection module being connected to said moving target estimation module.

9. The radar system of claim 1 wherein said systems formation module is a switching circuit forming a plurality of groupings of said SAR-processed signals, said MTI module being one of a plurality of MTI modules each receiving and operating on a respective one of said groupings of said SAR-processed signals.

10. The radar system of claim 9 wherein each of said MTI modules includes:

an adaptive weight computation submodule generating at least one complex weight value for each Doppler bin of each of the SAR-processed signals in the respective one of said groupings, said computation submodule being connected at an input to said systems formation module; and

a Hermitian product computation submodule connected at a first input to said adaptive weight module and at a second input to said systems formation module.

11. The radar system of claim 9 wherein each of said MTI modules is connected at an output to a moving target detection module.

12. The radar system of claim 11, further comprising a moving target estimation module, each of said MTI modules and said moving target detection module being connected to said moving target estimation module.

13. The radar system of claim 1, further comprising a stationary imaging computation module connected to at least one of said SAR modules for producing a signal encoding stationary objects.

14. The radar system of claim 13, further comprising a detection and estimation module connected to said stationary imaging computation module for detecting stationary objects and estimating associated parameters.

15. The radar system of claim 1 wherein at least one of said receivers is connected to a plurality of said signal delays having different delay values.

16. The radar system of claim 1 wherein said MTI module includes an adaptive weight computation submodule generating at least one complex weight value for each Doppler bin of each of the SAR-processed signals in said grouping, said computation submodule being connected at an input to said systems formation module, said MTI module further including a Hermitian product computation submodule connected at a first input to said adaptive weight module and at a second input to said systems formation module.

17. The radar system of claim 16 wherein said SAR modules consist of coarse SAR or range-Doppler processors for operating on short-dwell radar signals.

18. The radar system of claim 1 wherein said MTI module includes:

a spatial Fast Fourier Transform (FFT) submodule connected at an input to said systems formation module;

a beamspace subgrouping submodule connected at an input to said FFT submodule for forming Doppler beamspace subgroups of FFT transformed signals from said FFT module;

an adaptive weight computation submodule generating at least one complex weight value for each Doppler bin of each of the subgroup signals from said beamspace subgrouping submodule, said computation submodule being connected at an input to said beamspace subgrouping submodule; and

a Hermitian product computation submodule connected at a first input to said adaptive weight module and at a second input to said beamspace subgrouping submodule.

19. The radar system of claim 18 wherein said SAR modules consist essentially of coarse SAR or range-Doppler processors for operating on short-dwell radar signals.

20. The radar system of claim 1, wherein said MTI module is one of a plurality of MTI modules connected to said systems formation module, further comprising a moving target detection module, each of said MTI modules being connected at an output to said moving target detection module.

21. The radar system of claim 20, further comprising a moving target estimation module, each of said MTI modules and the moving target detection module being connected to said moving target estimation module.

22. The radar system of claim 21, further comprising a moving target imaging module connected at its input to outputs of the moving target detection module and moving target estimation module.

23. The radar system of claim 22 wherein the moving target imaging module is also operatively connected at its input to at least one pseudochannel signal.

24. The radar system of claim 1 where the arrangement of the transmit and receiving antennas is such that a displaced-phase-center-antenna condition is maintained for groups of pseudochannels.

25. The radar system of claim 1 wherein said MTI module is an adaptive moving target indication module.

26. The radar system of claim 1 wherein at least one of said signal delays is a zero delay.

27. The radar system of claim 1 wherein each of said receivers is operatively connected to at least two signal delays to produce at least two pseudochannels for each receiver channel, the signal delays being operatively connected to the respective SAR modules.

28. A radar signal processing method comprising:

transmitting from a moving platform a series of radio-frequency pulses toward a ground surface;

receiving, via an antenna structure mounted to said moving platform, radar signals reflected from stationary and moving objects;

digitizing the received radar signals;

operating on the digitzed radar signals to produce a plurality of pseudo-radar signals in respective pseudochannels;

processing the pseudo-radar signals to produce a plurality of SAR-processed signals;

forming or selecting at least one grouping of said SAR-processed signals; and

performing clutter suppression operations on said grouping of said SAR-processed signals.

29. The method of claim 28, further comprising:

forming a plurality of groupings of said SAR-processed signals; and

performing clutter suppression operations on each of said groupings of said SAR-processed signals.

30. The method of claim 29 wherein the performing of said clutter suppression operations includes:

generating a complex weight value for each contiguous range-azimuth sub-image of each of the SAR-processed signals in each of said groupings; and

computing a Hermitian product of the generated complex weight values and respective portions of the SAR-processed signals.

31. The method of claim 30 where the complex weight values are computed using an adaptive weight computation submodule to adaptively generate optimum weights.

32. The method of claim 28 wherein the operating on said delayed signals and said real-time signals includes performing a first stage of SAR processing, further comprising performing a second stage of SAR processing after performing of said clutter suppression operations on said grouping of said SAR-processed signals.

33. The method of claim 28 wherein the performing of said clutter suppression operations includes:

generating a complex weight value for each contiguous range-azimuth sub-image of SAR-processed signals in said grouping; and

computing a Hermitian product of the generated complex weight values and respective portions of the SAR-processed signals.

34. The method of claim 33 where the complex weight values are computed using an adaptive weight computation submodule to adaptively generate optimum weights.

35. The method of claim 28, further comprising:

performing detection operations on clutter-suppressed signals; and

performing estimation of target parameters for detected moving targets including the formation of moving target tracks.

36. The method of claim 35, further comprising:

performing moving target imaging using the available detection and estimation data along with the pseudochannel signals themselves.

37. The method of claim 28, further comprising:

performing stationary imaging of stationary objects; and

performing detection and estimation of stationary objects.

38. The method of claim 28, wherein the performing of said clutter suppression operation includes:

performing a spatial Fast Fourier Transform (FFT) on each of the SAR-processed signals in each of said groupings; and

forming Doppler-beamspace subgroups of FFT transformed signals; and

generating at least one adaptive complex weight vector per subgroup of the same dimension as each subgroup in each of said groupings; and

computing a Hermitian product of the generated adaptive complex weight vectors and respective portions of the subgroup signals.

39. A synthetic aperture moving target indication radar system, comprising:

a transmitting antenna connected to a radio frequency generator;

a plurality of a cardinality N>

1 of receiving antennas 1, . . . , n, . . . , N;

a plurality of said cardinality N of respective coherent radio frequency receivers connected to respective said receiving antennas;

a collection of sets of cardinalities K_n1 of signal delay taps 1, . . . , k, . . . K_n connected to feeds of respective said receiving antennas for creating time-displaced signals at delays t_l, . . . , t_k, . . . , t_Kn;

a plurality of said cardinality N>

1 of SAR processors operatively connected to respective said sets of signal delay taps for performing SAR processing on respective sets of said time-displaced received signals and outputting respective pluralities of said cardinality K_n of SAR processed time-displaced signals, each said processed time-displaced signal further comprising a plurality P_nk of outputs in Doppler bins 1, . . . , p, . . . P_nk;

a system formation module for selecting a group of a cardinality Z of subsets of cardinalities U_l, . . . , U_z, . . . , U_Z from a total possible collection of cardinality K_l+ . . . +K_n+ . . . +K_N of said SAR processed delayed signals; and

a plurality of a cardinality Z of MTI processing modules 1, . . . , z, . . . , Z for producing moving target indication output signals from each respective subset U_z of SAR processed delayed signals.

40. The radar system of claim 39 wherein said SAR processors further respectively comprise K_n SAR engines operatively connected in a parallel configuration to respective elements of a K_n-fold input comprising said time-displaced signals at delays t_l, . . . , t_k, . . . , t_Kn for implementing SAR processing algorithms to compress and focus said signals.

41. The radar system of claim 40 wherein said delays t_l, . . . , t_k, . . . , t_Kn are of form 0, . . . , (k−

1)T, . . . , (K_n−

1)T, for a fixed positive time interval T for all n.

42. The radar system of claim 40 wherein said P_nk are of form P_nk=P for a fixed cardinality P for all n.

43. The radar system of claim 39 wherein each said MTI processing module further comprises:

a splitter, for isolating a composite partial signal comprising a said output in an azimuth bin p from each of respective elements 1, . . . , u, . . . , U_z of said subsets U_z;

a plurality of said cardinality P of adaptive weight computation modules, for computing a complex adaptive weight wp vector from each of respective said partial signals; and

an plurality of cardinality P of Hermitian product modules for forming a complex inner product from each of respective adaptive weight vectors w_p and respective said composite signals, for forming a plurality of complex scalar outputs of the MTI processing module.

44. The radar system of claim 39 wherein each said MTI processing module z further comprises:

an FFT module, for performing a Fourier transform of an input data signal considered as a spatial signal indexed by a discrete spatial variable taking on values in 1, . . . , u, . . . , U_z in respective said doppler bins p drawn from a set of doppler bins 1, . . . p, . . . , P;

a Doppler-Beamspace Subgroup module for forming a set of a cardinality S_z of groups 1 . . . , s, . . . S_z of respective cardinalities M_s of outputs of said FFT module;

an plurality of said cardinality S_z of adaptive weight computation modules for computing a complex adaptive weight ws from each of respective said sets of cardinality M_s; and

an plurality of said cardinality S_z of Hermitian product modules for forming a complex inner product from each of respective adaptive weights w_s and each of respective said partial signals, for forming a plurality of complex scalar outputs of said MTI processing module.

45. A synthetic aperture moving target indication radar system, comprising:

a transmitting antenna connected to a radio frequency generator;

a plurality of cardinality N>

1 of receiving antennas 1, . . . , n, . . . , N connected to respective coherent radio frequency receivers;

a plurality of sets of cardinalities K_n1 of signal delay taps 1, . . . , k, . . . K_n connected to feeds of respective said receiving antenna for creating time-displaced signals of delays t_l, . . . , t_k, . . . , t_Kn

a plurality of said cardinality N of coarse SAR processing modules operatively connected to respective said sets of signal delay taps for producing sets of coarse Doppler image signals of a cardinality Q;

a system formation module connected to outputs of said plurality of coarse SAR processing modules for selecting a collection of a cardinality Z_Q of subsets of cardinalities U_l, . . . , U_z, . . . , U_Z of a total collection of size N x Q of said SAR processed delayed signals;

a plurality of a cardinality Z_Q of MTI processing modules 1, . . . , Z, . . . , Z_Q connected to outputs of said systems formation module for producing moving target indication output signals from each respective subset U_z of SAR processed delayed signals; and

a plurality of cardinality Z_Q of fine SAR processors for coherent_ly integrating respective Q-fold signal output from said MTI processing modules.