US5184134A
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US
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Fast phase difference autofocus
Assignee: Raytheon Co
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Filing: 1991-11-27
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Granted: 1993-02-02
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Expires: 2011-11-27
Abstract
Abstract A phase difference autofocus method that only requires one FFT for estimating a phase error in the entire synthetic array radar data. The phase difference autofocus method of the present invention automatically and efficiently estimates phase errors from radar signals, allowing a well focused SAR image to be produced. The present method comprises the following steps. First, each range bin is divided into two subarrays. Next, the two subarrays are complex-conjugate multiplied together to produce a cross spectrum of the two submaps produced by the subarrays. Then, the phases of each cross spectrum are aligned with an accumulated sum of the cross spectrums from previous processed range bins. The phase aligned cross spectrum is then added to the accumulated cross spectrum sum. All range bins are processed to get a final cross spectrum sum. Next, a single FFT is performed on the final cross spectrum sum to produce the cross correlation function. Then, the cross correlation function is magnitude-detected. Since the location of the peak of the cross correlation function is proportional to the phase error, a phase error estimate is obtained. Finally, the phase error correction signal is produced for the entire synthetic array radar data. Since only one FFT is performed during autofocus processing, the method is relatively fast.
Inventors
- 👤 Yoji G. Niho
- 👤 Eric W. Day
- 👤 Tammy L. Flanders
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 05:07
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/88; G01S13/89; G01S13/90; G01S13/9004; G01S13/9011; G01S13/9019
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
206 words
A fast phase difference autofocus method for removing phase errors from synthetic array radar signals, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; complex-conjugate multiplying the two subarrays together to produce a cross spectrum; determining a complex phasor for the cross spectrum to align its phase so that the cross spectrum can be coherently added to the accumulated sum of cross spectrums from previously processed range bins; multiplying the cross spectrum with the complex phasor and adding it to the accumulated sum of cross spectrums from previously processed range bins; repeating the previous three steps for all range bins to form the final cross spectrum sum from all range bins; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function and determining a peak location of the cross correlation function; multiplying the peak location by a scale factor to compute a center-to-end phase error estimate signal; and generating a phase error correction signal and removing the phase error from the synthetic array radar data by multiplying the data with the phase error estimate signal.
Claim 2
Dependent Claim
206 words
A fast phase difference autofocus method for removing phase errors from synthetic array radar signals, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; complex-conjugate multiplying the two subarrays together to produce a cross spectrum; determining a complex phasor for the cross spectrum to align its phase so that the cross spectrum can be coherently added to the accumulated sum of cross spectrums from previously processed range bins; multiplying the cross spectrum with the complex phasor and adding it to the accumulated sum of cross spectrums from previously processed range bins; repeating the previous three steps for all range bins to form the final cross spectrum sum from all range bins; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function and determining a peak location of the cross correlation function; multiplying the peak location by a scale factor to compute a center-to-end phase error estimate signal; and generating a phase error correction signal and removing the phase error from the synthetic array radar data by multiplying the data with the phase error estimate signal.
Claim 3
Dependent Claim
71 words
The method of claim 1 wherein the step of the determining the complex phasor to align the phase of the cross spectrum comprises the steps of: complex-conjugate multiplying the current cross spectrum and a previously accumulated sum of cross spectrums to produce a second order cross spectrum product; summing all terms of the second order cross spectrum product to form a complex sample; and extracting the phase of the complex sample.
Claim 4
Dependent Claim
211 words
A phase difference autofocus method for removing phase errors from synthetic array radar data, said method comprising the steps of: dividing a full array of each range bin in the synthetic array radar data into two subarrays; complex-conjugate multiplying the the two subarrays together to produce a cross spectrum; aligning the phases of a current cross spectrum with a presently accumulated cross spectrum sum by multiplying the current cross spectrum with a complex phasor and adding it to a presently accumulated cross spectrum sum; adding the current phase aligned cross spectrum to the previously accumulated cross spectrum sum to update the cross spectrum sum; whereby when all range bins have been processed, a final cross spectrum sum is produced; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT on the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function to detect a peak location of the cross correlation function; multiplying the filter location of the peak by a scale factor to compute a center-to-end phase error estimate signal; and generating a phase correction signal using the phase error estimate signal and removing the phase error from the synthetic array radar data by multiplying the data with the phase estimate signal.
Claim 5
Dependent Claim
211 words
A phase difference autofocus method for removing phase errors from synthetic array radar data, said method comprising the steps of: dividing a full array of each range bin in the synthetic array radar data into two subarrays; complex-conjugate multiplying the the two subarrays together to produce a cross spectrum; aligning the phases of a current cross spectrum with a presently accumulated cross spectrum sum by multiplying the current cross spectrum with a complex phasor and adding it to a presently accumulated cross spectrum sum; adding the current phase aligned cross spectrum to the previously accumulated cross spectrum sum to update the cross spectrum sum; whereby when all range bins have been processed, a final cross spectrum sum is produced; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT on the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function to detect a peak location of the cross correlation function; multiplying the filter location of the peak by a scale factor to compute a center-to-end phase error estimate signal; and generating a phase correction signal using the phase error estimate signal and removing the phase error from the synthetic array radar data by multiplying the data with the phase estimate signal.
Claim 6
Dependent Claim
228 words
A phase difference autofocus method that removes phase errors from synthetic array radar data, said method comprising the steps of: dividing a full array from each range bin of the synthetic array radar data into two subarrays X n (m), Y n (m) of length M; complex-conjugate multiplying the two subarrays together to produce a cross spectrum r n (m); computing a phasor e jyn by complex-conjugate multiplying the cross spectrum r n (m) with the presently accumulated sum SUM n-1 (m), adding all terms of the resulting product, and then extracting its phase y n to form the phasor e jyn ; integrating the phase aligned cross spectrum r n (m) e jyn across all range bins to produce a cross spectrum sum comprising a summed value SUM n (m)=SUM n-1 (m)+r n (m) e jyn , applying an amplitude weighting function to the cross spectrum sum SUM N (m); performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function to determine the location t xy of the peak response therein; computing a quadratic phase error estimate φ q =-2p t xy M 2 /(4LK); generating a phase error correction signal e j φq (m/M)2, -M<m<M; and removing the phase error from the synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 7
Dependent Claim
228 words
A phase difference autofocus method that removes phase errors from synthetic array radar data, said method comprising the steps of: dividing a full array from each range bin of the synthetic array radar data into two subarrays X n (m), Y n (m) of length M; complex-conjugate multiplying the two subarrays together to produce a cross spectrum r n (m); computing a phasor e jyn by complex-conjugate multiplying the cross spectrum r n (m) with the presently accumulated sum SUM n-1 (m), adding all terms of the resulting product, and then extracting its phase y n to form the phasor e jyn ; integrating the phase aligned cross spectrum r n (m) e jyn across all range bins to produce a cross spectrum sum comprising a summed value SUM n (m)=SUM n-1 (m)+r n (m) e jyn , applying an amplitude weighting function to the cross spectrum sum SUM N (m); performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function to determine the location t xy of the peak response therein; computing a quadratic phase error estimate φ q =-2p t xy M 2 /(4LK); generating a phase error correction signal e j φq (m/M)2, -M<m<M; and removing the phase error from the synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 8
Dependent Claim
136 words
A phase difference autofocus method that removes phase errors from synthetic array radar data, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; producing a cross spectrum of the two subarrays; aligning the phases of each cross spectrum with an accumulated sum of cross spectrums; adding the phase aligned cross spectrum to the accumulated cross spectrum sum; processing all range bins to compute a final cross spectrum sum; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT on the amplitude weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function; producing a phase error correction signal; and removing the phase error from synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 9
Dependent Claim
136 words
A phase difference autofocus method that removes phase errors from synthetic array radar data, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; producing a cross spectrum of the two subarrays; aligning the phases of each cross spectrum with an accumulated sum of cross spectrums; adding the phase aligned cross spectrum to the accumulated cross spectrum sum; processing all range bins to compute a final cross spectrum sum; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT on the amplitude weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function; producing a phase error correction signal; and removing the phase error from synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 10
Dependent Claim
249 words
A fast phase difference autofocus method for removing phase errors from synthetic array radar signals, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; complex-conjugate multiplying the two subarrays together to produce a cross spectrum; determining a complex phasor for the cross spectrum to align its phase so that the cross spectrum can be coherently added to the accumulated sum of cross spectrums from previously processed range bins by: complex-conjugate multiplying the current cross spectrum and a previously accumlated sum of cross spectrums to produce a second order cross spectrum product; summing all terms of the second order cross spectrum product to form a complex sample; and extracting the phase of the complex sample; multiplying the cross spectrum with the complex phasor and adding it to the accumulated sum of cross spectrums from previously processed range bins; repeating the process over all range bins to form the final cross spectrum sum from all range bins; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function and determining a peak location of the cross correlation function; multiplying the peak location by a scale factor to compute a center-to-end phase error estimate; and generating a phase error correction signal and removing the phase error from the synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 11
Dependent Claim
249 words
A fast phase difference autofocus method for removing phase errors from synthetic array radar signals, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; complex-conjugate multiplying the two subarrays together to produce a cross spectrum; determining a complex phasor for the cross spectrum to align its phase so that the cross spectrum can be coherently added to the accumulated sum of cross spectrums from previously processed range bins by: complex-conjugate multiplying the current cross spectrum and a previously accumlated sum of cross spectrums to produce a second order cross spectrum product; summing all terms of the second order cross spectrum product to form a complex sample; and extracting the phase of the complex sample; multiplying the cross spectrum with the complex phasor and adding it to the accumulated sum of cross spectrums from previously processed range bins; repeating the process over all range bins to form the final cross spectrum sum from all range bins; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function and determining a peak location of the cross correlation function; multiplying the peak location by a scale factor to compute a center-to-end phase error estimate; and generating a phase error correction signal and removing the phase error from the synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 12
Dependent Claim
217 words
A fast phase difference autofocus method generating a phase error correction signal that is used to remove phase errors from synthetic array radar signals, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; complex-conjugate multiplying the two subarrays together to produce a cross spectrum; determining a complex phasor for the cross spectrum to align its phase so that the cross spectrum can be coherently added to the accumulated sum of cross spectrums from previously processed range bins; multiplying the cross spectrum with the complex phasor and adding it to the accumulated sum of cross spectrums from previously processed range bins; repeating the previous three steps for all range bins to form the final cross spectrum sum from all range bins; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function and determining a peak location of the cross correlation function; multiplying the peak location by a scale factor to compute a center-to-end phase error estimate; and generating a phase error correction signal that is adapted to remove the phase error from the synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 13
Dependent Claim
217 words
A fast phase difference autofocus method generating a phase error correction signal that is used to remove phase errors from synthetic array radar signals, said method comprising the steps of: dividing each range bin of the synthetic array radar data into two subarrays; complex-conjugate multiplying the two subarrays together to produce a cross spectrum; determining a complex phasor for the cross spectrum to align its phase so that the cross spectrum can be coherently added to the accumulated sum of cross spectrums from previously processed range bins; multiplying the cross spectrum with the complex phasor and adding it to the accumulated sum of cross spectrums from previously processed range bins; repeating the previous three steps for all range bins to form the final cross spectrum sum from all range bins; applying an amplitude weighting function to the final cross spectrum sum; performing an FFT to the amplitude-weighted cross spectrum sum to produce a cross correlation function; magnitude-detecting the cross correlation function and determining a peak location of the cross correlation function; multiplying the peak location by a scale factor to compute a center-to-end phase error estimate; and generating a phase error correction signal that is adapted to remove the phase error from the synthetic array radar data by multiplying the data with the phase error correction signal.
Claim 14
Dependent Claim
71 words
The method of claim 7 wherein the step of the determining the complex phasor to align the phase of the cross spectrum comprises the steps of: complex-conjugate multiplying the current cross spectrum and a previously accumulated sum of cross spectrums to produce a second order cross spectrum product; summing all terms of the second order cross spectrum product to form a complex sample; and extracting the phase of the complex sample.
References Cited (Backward Citations)
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