Method of motion compensation in synthetic aperture radar target imaging and a system for performing the method

Claim 3

A method according to claim 1, characterized in that the digital processing of the signals received comprises the following steps: (a) bandpass filtration of a signal received from a target, (b) calculation of a complex representation of the received signal by means of a Hilbert transformation to provide a complex signal, (c) frequency-shift and decimation of the complex signal thus obtained, (d) bandpass filtration of the frequency-shifted and decimated complex signal to isolate the reference signal contained, (e) complex conjugation of the transponder signal, and multiplication of the complex signal obtained in (b) by the complex conjugated transponder signal, (f) bandpass filtration of signal resulting from said multiplication and decimation of said bandpass filtered signal, (g) performance of a Fast Fourier transformation on the said bandpass filtered and decimated signal to produce a spectrum showing the distribution of reflection contributions across the target.

Claim 4

A synthetic aperture radar system comprising a synthetic aperture radar, said radar transmitting a signal toward a target, and comprising a transponder mounted on the target, said transponder transmitting a modulated, coherent copy of the signal transmitted toward the target, and comprising a receiver to receive a reflected radar signal and the transponder signal, characterized in that the system further comprises: (a) transponder means for frequency shifting of the signal transmitted toward the target so that in terms of frequency it is completely outside the region where doppler information may be expected in the radar signal reflected from the target, (b) separating means separating the reflected radar signal and the transponder signal immediately upon reception, and (c) combination means for combining the reflected radar signal and the transponder signal so as to compensate for the translatory motion of the target and fluctuations in the propagation paths of the signals whereby to remove translatory doppler components of said combined signal.

Claim 5

A synthetic aperture radar system comprising a synthetic aperture radar, said radar transmitting a signal toward a target, and comprising a transponder mounted on the target, said transponder transmitting a modulated, coherent copy of the signal transmitted toward the target, and comprising a receiver to receive a reflected radar signal and the transponder signal, characterized in that the system further comprises: (a) transponder means for frequency shifting of the signal transmitted toward the target so that in terms of frequency it is completely outside the region where doppler information may be expected in the radar signal reflected from the target, (b) separating means separating the reflected radar signal and the transponder signal immediately upon reception, and (c) combination means for combining the reflected radar signal and the transponder signal so as to compensate for the translatory motion of the target and fluctuations in the propagation paths of the signals whereby to remove translatory doppler components of said combined signal.