Efficient adaptive filter bank

• US 4,652,881 A
• Filed: 01/10/1984
• Issued: 03/24/1987
• Est. Priority Date: 01/10/1984
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Lewis, Bernard L.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Gregory, Bernarr Earl
• Application Number:
  US06/569,685
• Time in Patent Office: 1,169 Days
• Field of Search: 343/5 CE, 343/5 FT, 343/5 NQ, 343/7.7, 343/374, 343/375, 343/17.2 PC, 343/18 E, 343/5 SW, 364/724, 364/726, 364/825, 364/827
• US Class Current: 342/160
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242

Abstract

An N-point Fourier transform circuit for a moving target indicator system including a delay circuit with 2N-2 delays, N frequency filters, a processor for forming a main signal and N-1 auxiliary signals via time sample manipulation, a Gram-Schmidt adaptive canceller circuit for decorrelating the N-1 auxiliary signals from the main signal, and a first and second commutating switches. The first switch tracks a given set of N time samples through the delay circuit. The second switch switches the given set of N time samples through a different successive frequency filters of the N frequency filters every transmission. The first switch tracks in synchronism with the second switch and switches to obtain a new given set of N time samples every NT seconds.

Claims

1. An N-point Fourier transform circuit for a moving target indication system with signal interpulse period of T, comprising:

a delay circuit for taking a plurality of adjacent time samples of a signal, taken T seconds apart;

N frequency filters, with each frequency filter comprising N parallel time sample lines, with each time sample line having an input, an output, and a phase shifter disposed therein;

a processor for forming a main signal via time sample addition and N-1 auxiliary signals via various time sample additions and subtractions of the N time samples from the output lines of a given frequency filter;

an adaptive canceller for decorrelating said N-1 auxiliary signals from said main signal;

a first switching circuit for tracking a given set of N time samples through said delay circuit; and

a second switching circuit for switching said given set of N time samples through successive frequency filters on successive transmissions;

wherein said first switching circuit switches in synchronism with said second switching circuit, said first switching circuit obtaining a new given set of N time samples every NT seconds.

2. An N-point Fourier transform circuit as defined in claim 1, wherein said second switching circuit is disposed to switch said processor from frequency filter output to frequency filter output on successive transmissions;

and

said first switching circuit provides said given set of N time samples to at least one frequency filter at a time.

3. An N-point Fourier transform circuit as defined in claim 2, wherein said delay circuit comprises 2N-2 delay elements, each with a delay T, and with a signal tap before each delay element and after the last delay element.

4. An N-point Fourier transform circuit as defined in claim 3, wherein said first switch is an N-pole, 2N-1 position commutating switch for switching said given set of N adjacent time samples from said delay circuit to said frequency filters, wherein said first switch shifts its N poles one tap every T seconds and repeats every NT seconds.

5. An N-point Fourier transform circuit as defined in claim 4, wherein said second switch is an N pole N² -position switch which shifts N positions to the next adjacent frequency filter every T seconds and repeats every NT seconds.

6. An N-point Fourier transform circuit as defined in claim 5, wherein said adaptive canceller is a Gram-Schmidt adaptive canceller.

7. An N-point Fourier transform circuit as defined in claim 1, wherein said first switching circuit is connected to said second switching circuit;

and

said second switching circuit switches said given set of N time samples from frequency filter to frequency filter on successive transmissions.

8. An N-point Fourier transform circuit as defined in claim 7, wherein said delay circuit comprises 2N-2 delay elements, each with a delay T, and with a signal tap before each delay element and after the last delay element.

9. An N-point Fourier transform circuit as defined in claim 8, wherein said first switch is an N-pole, 2N-1 position commutating switch for switching said given set of N adjacent time samples from said delay circuit to said frequency filters, wherein said first switch shifts its N poles one tap every T seconds and repeats every NT seconds.

10. An N point Fourier transform circuit as defined in claim 9, wherein said second switch is an N-pole N² -position switch which shifts N positions to the next adjacent frequency filter every T seconds and repeats every NT seconds.

11. An N-point Fourier transform circuit as defined in claim 10, wherein said adaptive canceller is a Gram-Schmidt adaptive canceller.

12. An N-point Fourier transform circuit for separating stationary echoes from moving targets in a moving target indication system with a signal interpulse period of T, comprising:

a delay circuit for taking 2N-1 adjacent time samples of an MTI signal, taken T seconds apart;

N frequency filter sets of parallel phase shifters, with N phase shifters and attendant time sample output lines for each set;

an N-pole, 2N-1 position first commutating switch for commutatively selecting a given N adjacent time samples from said delay circuit for application to at least one frequency filter set of N phase shifters;

an N pole, N² -position second commutating switch for commutatively selecting successive discrete frequency filter sets of phase shifted time sample outputs from said N frequency filter sets of phase shifters every T seconds;

a processor for forming a main signal via time sample addition and N-1 auxiliary signals via various additions and subtractions from a given discrete frequency filter set of N phase shifted time sample output lines; and

an adaptive canceller for decorrelating said N-1 auxiliary signals from said main signal;

wherein said first switch switches in synchronism with said second switch to provide said given N adjacent time samples to the frequency filter set of phase shifters to which said processor is connected, said first switch changing to a new given N adjacent time samples every NT seconds.

13. An N-point Fourier transform circuit as defined in claim 12, wherein said delay circuit comprises 2N-2 delay elements, each with a delay T, and with a signal tap before each delay element and after the last delay element, wherein said first commutating switch shifts its N poles one tap every T seconds and repeats every NT seconds, while said second commutating switch shifts N positions to a different discrete set of phase shifter output lines every T seconds and repeats every NT seconds.

14. An N-point Fourier transform circuit as defined in claim 13, wherein said adaptive canceller is a Gram-Schmidt adaptive canceller.

15. An N-point Fourier transform circuit as defined in claim 14, wherein said N-pole first switch has the nth pole thereof connected to nth phase shifter for each of said N frequency filter phase shifter sets, where 1≦

n≦

N.

16. A method for separating moving targets from non or slowly moving clutter wherein a plurality of adjacent time samples of a signal are taken T seconds apart, where T is the interpulse period, further including a bank of N frequency filters, a processor for forming a main signal and N-1 auxiliary signals from N time samples, and an adaptive canceller for decorrelating said N-1 auxiliary signals from said main signal, said method comprising the steps of:

switching a given set of N time samples of said signal to at least one frequency filter in said bank of frequency filters;

switching said processor from frequency filter output to frequency filter output every T seconds;

wherein said first switching step switches in synchronism with said second switching step to provide said given set of N time samples to the frequency filter in said bank to which said processor is connected; and

switching to a new set of N time samples for application to said bank of frequency filters every NT seconds.

17. A method as defined in claim 16, further comprising the step of taking 2N-1 time samples of said signal.

18. A method as defined in claim 17, comprising the step of utilizing said adaptive canceller to perform Gram-Schmidt processing to decorrelate said N-1 auxiliary signals from said main signal.

19. An N-point Fourier transform circuit for a moving target indication system with a signal interpulse period of T, comprising:

a delay circuit for taking a plurality of adjacent time samples of a signal, taken T seconds apart;

N frequency filters, with each frequency filter comprising N parallel time sample lines, with each time sample line having an input, an output, and a phase shifter disposed therein;

a processor connected to the outputs of said N frequency filters for forming a main signal via time sample addition and N-1 auxiliary signals via various time sample additions and subtractions of the N time samples from the output lines of a given frequency filter;

an adaptive canceller for decorrelating said N-1 auxiliary signals from said main signal;

a first switching circuit for tracking a given set of N time samples through said delay circuit;

a second switching circuit for switching said given set of N time samples from frequency filter to frequency filter on successive transmissions;

wherein said first switching circuit switches in synchronism with said second switching circuit, said first switching circuit obtaining a new given set of N time samples every NT seconds.

20. An N-point Fourier transform circuit as defined in claim 19, wherein said delay circuit comprises 2N-2 delay elements, each with a delay T, and with a signal tap before each delay element and after the last delay element.

21. An N-point Fourier transform circuit as defined in claim 20, wherein said first switch is an N-pole, 2N-1 position commutating switch for switching said given set of N adjacent time samples from said delay circuit to said second switch, wherein said first switch shifts its N poles one tap every T seconds and repeats every NT seconds.

22. An N-point Fourier transform circuit as defined in claim 21, wherein said second switch is an N-pole N² -position switch which shifts N positions to the next adjacent frequency filter every T seconds and repeats every NT seconds.

23. An N-point Fourier transform circuit as defined in claim 22, wherein said adaptive canceller is a Gram-Schmidt adaptive canceller.

24. A method for separating moving targets from non or slowly moving clutter including a delay circuit for taking 2N-1 adjacent time samples of a signal T seconds apart, where T is the interpulse period, further including a bank of N frequency filters, a processor connected to said filter bank for forming a main signal and N-1 auxiliary signals from N time samples, and an adaptive canceller for decorrelating said N-1 auxiliary signals from said main signal, said method comprising the steps of:

tracking a given set of N time samples of said MTI signal through said delay circuit;

switching said given set of N time samples from frequency filter to frequency filter every T seconds;

wherein said tracking step operates in synchronism with said switching step; and

commutating to a new set of N time samples to be tracked through said delay circuit every NT seconds.

25. A method as defined in claim 24, comprising the step of utilizing said adaptive canceller to perform Gram-Schmidt processing to decorrelate said N-1 auxiliary signals from said main signal.