Synthetic aperture radars including moving target indication

Claim 1

A synthetic aperture radar system for surveying a region from a moving location including an aerial having a plurality of space sections, a transmitter adapted to cooperate with said aerial to project a series of emitted pulses towards said region, a receiver adapted to cooperate with said aerial to receive corresponding echo pulses relating to targets in said region, the arrangement being such that a first emitted pulse is projected from, and corresponding first echo pulses are received at, at least one of said sections, a second emitted pulse is projected from, and corresponding second echo pulses are received at, at least one other of said sections at different times but at substantially the same position in relation to a predetermined frame of reference and the sequence is repeated at a first predetermined repetition frequency, processing means for comparing corresponding first and second echo pulses to substantially cancel those echo pulses relating to targets, which have not moved in relation to the frame of reference in the time elapsed between the emission of the corresponding first and second echo pulses and to provide signals at a second predetermined repetition frequency related to the first repetition frequency, indicative of the doppler frequency shift of the pulses relating to other targets and correlator circuit means arranged to correlate those of said signals lying within a specific total frequency band with a predetermined correlation function to provide indications of the positions of said other targets, wherein the said second repetition frequency is selected to be substantially equal to the spread of said specific total frequency band.