Technique for implementing very large pulse compression biphase codes

• US 6,020,843 A
• Filed: 03/30/1999
• Issued: 02/01/2000
• Est. Priority Date: 03/30/1999
• Status: Expired due to Fees

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Rosen, Robert A., Krikorian, Kapriel V.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/281,679
• Time in Patent Office: 308 Days
• Field of Search: 342/25, 342/175, 342/189-197, 342/202-204, 375/358
• 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
• CPC Class Codes: G01S 7/285 Receivers

Abstract

A processing method for use in providing improved SAR imagery at high duty factors that provides for enhanced radar sensitivity. Radar signals are transmitted that embody a high duty factor ultra-high resolution SAR waveform generated using a biphase code with a predetermined high pulse compression ratio. Received radar returns comprising a SAR map are Fourier transformed and multiplied by a stored set of complex weights. The resultant Fourier transformed complex weighted SAR map is then inverse Fourier transformed to obtain compressed range bins. The inverse Fourier transformed SAR map is then processed for display.

Claims

1. A method for use in a synthetic array radar system comprising the steps of:

transmitting radar signals comprising a SAR waveform having a predetermined duty factor and resolution generated using a biphase code with a predetermined pulse compression ratio;

intrapulse Fourier transforming received radar returns comprising a SAR map;

multiplying the intrapulse Fourier transformed SAR map by a stored set of complex weights;

inverse Fourier transforming the weighted SAR map to obtain compressed range bins that correspond to a SAR map having enhanced sensitivity.

2. The method recited in claim 1 further comprising the step of processing received radar returns comprising the SAR map using motion compensation phase adjustment processing to provide a motion compensated SAR map.

3. The method recited in claim 2 further comprising the step of resampling the motion compensated SAR map.

4. The method recited in claim 1 wherein the stored weights comprise a weighted inverse of the spectrum of the biphase code.

5. The method recited in claim 1 wherein the weights comprise a modified set of Dolph-Chebyshev weights.

6. The method recited in claim 1 further comprising the step of low pass filtering the Fourier transformed and complex weighted SAR map to reduce the number of range bins.

7. The method recited in claim 1 further comprising the step of polar formatting the weighted transformed SAR map before the inverse Fourier transforming step.

8. The method recited in claim 1 wherein the complex weights are calculated by taking the reciprocal of the Fourier transform of the biphase code and multiplying by a modified set of Dolph-Chebyshev weights.

9. The method recited in claim 1 wherein the complex weights are optimized for range sidelobe performance, resolution and weighting loss.

10. The method recited in claim 1 wherein the complex weights that are optimized for range sidelobe performance, resolution and weighting loss.

11. A method for use in a synthetic array radar system comprising the steps of:

transmitting radar signals comprising a SAR waveform having a predetermined duty factor and resolution generated using a biphase code with a predetermined pulse compression ratio;

processing received radar returns comprising a SAR map using motion compensation phase adjustment processing to provide a motion compensated SAR map;

intrapulse Fourier transforming the motion compensated SAR map;

multiplying the intrapulse Fourier transformed SAR map by a stored set of complex weights;

inverse Fourier transforming the weighted SAR map to obtain compressed range bins that correspond to a SAR map having enhanced sensitivity; and

processing the SAR map for display.

12. The method recited in claim 11 further comprising the step of resampling the motion compensated SAR map.

13. The method recited in claim 11 wherein the stored weights comprise a weighted inverse of the spectrum of the biphase code.

14. The method recited in claim 11 wherein the weights comprise a modified set of Dolph-Chebyshev weights.

15. The method recited in claim 11 further comprising the step of low pass filtering the Fourier transformed and complex weighted SAR map to reduce the number of range bins.

16. The method recited in claim 11 further comprising the step of polar formatting the weighted transformed SAR map before the inverse Fourier transforming step.

17. The method recited in claim 11 wherein the complex weights are calculated by taking the reciprocal of the Fourier transform of the biphase code and multiplying by a modified set of Dolph-Chebyshev weights.