The Phase Gradient Autofocus (PGA) algorithm

has been widely used in Spotlight Synthetic Aperture

Radar (SAR) to remove motion-induced blurs in the

images. The PGA algorithm has been proven to be a superior

autofocus method. PGA assumes a narrow beam,

which is valid for most SAR systems. However, lower altitude

SA& have large range dependencies that cannot be

ignored. A new phase estimator for PGA is introduced

and extended to allow range dependence. An ERS-1 image

of Death Valley is used in simulations comparing the

new estimator to the widely used maximum likelihood approach

and in demonstrating the range-dependent PGA

algorithm.