Abstract

A radar transmission, reception and signal processing system generates high esolution synthetic aperture radar ground maps from air or space platforms using waveforms in which frequency is changed pulse-to-pulse. The transmitted radar signal is comprised of a series N bursts with n pulses per burst wherein each of the pulses is a fixed frequency step, Ɗf, either above or below one or the other of the n pulses, i.e. the n pulses comprises an ordered set and further, preferably, wherein the set of n pulses is arranged in time as a random permutation of the ordered set. In each of the k sample gates for each burst the n complex samples of reflectivity are inverse Fourier transformed from frequency domain samples of reflectivity to synthetic range domain profiles to result in an array of aligned range profiles in each of k coarse range delay positions. Azimuth or cross-range processing is accomplished by convolving complex range data appearing in each synthetic range cell with a suitable azimuth reference to result in a set of complex numbers that represent complex reflectivity maps of the earth's surface in that coarse range bin."Zoom" capability is achieved by discrete Fourier transforming the data in each synthetic range cell of the selected delay. "Zoom" is achieved by increasing the target dwell time and simultaneously increasing the radar signal bandwidth.In both the spotlight "zoom" mode and the SAR mode, the processed data is converted from complex numbers to absolute magnitudes before display.