Synthetic aperture radar image formation

The implementation of a subaperture technique for image formation in a synthetic aperture radar system (SAR) is presented. Coherent subaperture techniques for SAR image formation involved partitioning the data (in the time domain) into subapertures. The data in each subaperture are used to form low-resolution images which are combined coherently to form the final high-resolution image. The subaperture technique whose implementation is presented is referred to as the step transform. In the theoretical development, it was assumed that the received target signal had a perfectly linear slope in the frequency versus time plane. However, in practice there are quadratic, cubic, and higher-order phase-error terms in the phase of the received signal. The phase-error terms need to be removed in order to form a well-focused SAR image, and the phase correction can be more easily performed with a subaperture image-formation technique like the step transform rather than processing the whole aperture by itself