Second order motion compensator for high resolution radar

• US 4,034,370 A
• Filed: 04/06/1976
• Issued: 07/05/1977
• Est. Priority Date: 08/23/1972
• Status: Expired due to Term

• Current Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Mims, James H.
• Primary Examiner(s): Tubbesing, T.H.
• Application Number:
  US05/674,181
• Time in Patent Office: 455 Days
• Field of Search: 343/5 CM, 343/5 DP
• US Class Current: 342/25.00D
• CPC Class Codes: G01S 13/9011 with frequency domain processing of the SAR signals in azimuth G01S13/9005 takes precedence

Abstract

A method and apparatus for providing motion compensation that allows dynamically changing flight paths during high resolution, squinted, synthetic aperture mapping by making use of a second order motion compensation by means of a two-stage correlator configuration utilizing digital signal processing techniques.

Claims

1. Method of providing motion compensation for target data in a synthetic aperture radar comprising the steps of:

sequentially transmitting and receiving a plurality of radar pulses during a coherent integration time period, said radar pulses having a predetermined interpulse period and providing analog signals therefrom;

converting each analog signal into complex digital data samples corresponding to a predetermined number of respective range cells during said coherent integration time period;

performing a first time correction and phase shift on each of said complex digital data samples thereby effecting a first order motion compensation thereon;

sequentially entering said complex digital data samples into a memory in sets of digital data time samples for a selected number of interpulse periods;

sequentially feeding each set of time samples as a data block into a digital correlator and performing a digital integration to resolve said data block into data reflective of a respective plurality of frequency bands which correspond to synthetic subbeams;

performing a second time shift and phase correction on each data reflective of each synthetic subbeam thereby effecting a second order motion compensation thereon;

sequentially feeding data samples for each plurality of synthetic subbeams into a memory in selected sets of range cells;

feeding out data samples for each synthetic subbeam over a predetermined number of interpulse periods as a data block into another digital correlator and performing a digital integration to resolve each synthetic subbeam into data reflective of a respective plurality of frequency bands which correspond to motion compensated azimuth cells; and

feeding data reflective of said motion compensated azimuth cells to synthetic aperture radar display apparatus.

2. The method as defined by claim 1 wherein said step of performing a digital integration comprises the step of performing a discrete Fourier transform.

3. The method as defined by claim 1 wherein said step of performing a digital integration comprises the step of performing the fast Fourier transform.

4. The method as defined by claim 3 wherein said step of performing the fast Fourier transform comprises providing transformations on overlapping data blocks where said overlapping ranges between 50 and 75%.

5. The method as defined by claim 1 wherein said step of performing a digital integration comprises a time frequency decimation process during said coherent integration time.

7. The apparatus as defined by claim 5 wherein said first and second memory comprises a "corner-turn" memory.

12. The apparatus as defined by claim 7 wherein said second digital memory comprises a triangular memory configuration wherein M×

NF1 data blocks are entered on one axis and the N×

N2 data blocks is fed out from another axis with means for shifting of data samples progressively from input to output.

6. Apparatus for digitally providing motion compensation for vehicle maneuverability in a synthetic aperture radar coupled to the navigational system of said vehicle and including a transmitter and receiver section which respectively transmit and receive a sequence of N radar pulses during a predetermined coherent integration time period and converts the return pulses into a respective number of I&

Q analog video signals, the combination comprised of;

means coupled to said receiver section for converting each of said I&

Q analog video signals into M complex digital range samples;

first order motion compensation means, coupled to and receiving information from said navigational system, connected to said converting means and including means for applying a selective time translation and phase shift to each of said M digital samples;

a first digital data memory coupled to said converting means for storing M data blocks of digital samples where each data block includes time samples covering a selected number of N'"'"' of interpulse periods during said coherent integration time;

a digital processor adapted to perform a time-frequency decimation on a digital data block coupled to said memory, being operable to sequentially receive each of said M data blocks and resolve each data block into a plurality of frequency bands which corresponds to NF1 synthetic subbeams;

second order motion compensation means, coupled to and receiving information from said navigational system, connected to said digital processor and including means for applying another selected time translation and phase shift to each frequency band;

a second digital data memory coupled to said second order motion compensation means for storing digital data samples for M= NF1 synthetic subbeams for a selected number N2 time intervals and feed out sequential data blocks of M×

N2 into data samples; and

a second digital processor adapted to perform a time-frequency decimation process on a data block coupled to said second memory, being operable to sequentially receive each data block therefrom and resolve each said data block into a plurality of frequency bands in the azimuth direction which correspond to motion compensated range cells adaptable for utilization by a synthetic aperture radar display unit.

8. The apparatus as defined by claim 6 wherein said converting means comprises a time multiplex analog to digital converter.

9. The apparatus as defined by claim 6 wherein the first and second recited digital processor comprises a correlator operable as an integrating digital filter bank.

10. The invention as defined by claim 6 wherein the first and second recited digital processor comprises apparatus implemented to perform the Discrete Fourier Transform algorithm.

11. The apparatus as defined by claim 10 wherein said processors are implemented to perform the Fast Fourier Transform algorithm.