Signal processor for synthetic aperture radar, particularly for parallel computation

Claim 1

A method of focussing in a synthetic aperture radar system, comprising the steps of: (a) transmitting a radar signal to a target and recovering a radar echo with complex in-phase and quadrature components; (b) sampling said complex radar echo at a frequency f S ; (c) filtering the sampled complex radar echo through N bandpass filters with identical transfer functions and centered around equispaced center frequencies f i to obtain an output from each filter; (d) effecting base-band translation of each filter output so that the center frequency f i of the respective pass band corresponds to zero frequency; (e) undersampling each signal resulting form the base-band translation to yield N complex signals U ai sampled at f S /N; (f) delaying each of the signals U ai by a number of sampling steps correlated with a respective reference signal R i related to the corresponding frequency band to yield focussed signals U f1 through U fN of limited resolution individually, and deriving said respective reference signals by base-band translation and undersampling of a signal representing a system response of the radar signal to a point scatterer and pass band filtered with a filter having a pass band corresponding to that of the filter producing the respective signal U ai ; and (g) additively combining the signals U f1 through U fN into M groups of signals where M<N, to yield at least one signal of a resolution 1/M times a theoretical maximum resolution, said reference signals being derived in step (f) by beating the response of the radar signal to a point scatterer with an exp complex sinusoidal waveform with a j2 fit at zero frequency and subjecting the beat signals to filtering and base-band translation to yield the respective signals R i .

Claim 2

A method of focussing in a synthetic aperture radar system, comprising the steps of: (a) transmitting a radar signal to a target and recovering a radar echo with complex in-phase and quadrature components; (b) sampling said complex radar echo at a frequency f S ; (c) filtering the sampled complex radar echo through N bandpass filters with identical transfer functions and centered around equispaced center frequencies f i to obtain an output from each filter; (d) effecting base-band translation of each filter output so that the center frequency f i of the respective pass band corresponds to zero frequency; (e) undersampling each signal resulting form the base-band translation to yield N complex signals U ai sampled at f S /N; (f) delaying each of the signals U ai by a number of sampling steps correlated with a respective reference signal R i related to the corresponding frequency band to yield focussed signals U f1 through U fN of limited resolution individually, and deriving said respective reference signals by base-band translation and undersampling of a signal representing a system response of the radar signal to a point scatterer and pass band filtered with a filter having a pass band corresponding to that of the filter producing the respective signal U ai ; and (g) additively combining the signals U f1 through U fN into M groups of signals where M<N, to yield at least one signal of a resolution 1/M times a theoretical maximum resolution, said reference signals being derived in step (f) by beating the response of the radar signal to a point scatterer with an exp complex sinusoidal waveform with a j2 fit at zero frequency and subjecting the beat signals to filtering and base-band translation to yield the respective signals R i .