True Time-Delay Minimum Entropy Autofocus Using a 2D Phase Error Overcomplete Basis

In previous work [1], [2], we developed SAR autofocus approaches capable of correcting for residual motion compensation errors exceeding a range resolution cell by applying 2D autofocus corrections in the spatial frequency domain that approximate pulse-level true time-delay motion compensation corrections. In this article we improve upon the approximations employed in our previous work, enabling the ability to estimate and compensate for large motion compensation errors (exceeding a resolution cell) by estimating and applying time-delays at the true pulse level to a complex SAR image. Our approach is based on minimizing entropy and exploits an overcomplete basis for the possible motion compensation errors to aid in convergence of the optimization.