High quality focused SAR imaging dictates that the relative phase error over an aperture must be kept below a fraction of
a wavelength. On most deployed SAR systems the internal measurement systems ability to measure position uncertainty
is not sufficient to achieve this required precision. This necessitates an additional post-processing step of data-driven
phase error mitigation known as autofocus. We present results comparing the performance of a variety of autofocus
techniques including image metric optimization based techniques and several variants of phase gradient autofocus (PGA).
The degree of focusing is evaluated with an image focus metric, specific to SAR images, that is not biased toward any
particular autofocus algorithm. This evaluation is performed on a variety of scene types using injected (known) phase
errors. We show that PGA autofocus outperforms the image metric optimization techniques tested (based on minimizing
image entropy) in low contrast SAR scenes.