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In previous descriptions of the step transform SAR azimuth compression algorithm, it has been assumed that the azimuth signal is linear FM and is strictly confined within a single range cell. These conditions do not always hold. Under stringent imaging conditions range curvature occurs, i.e., a nonlinear range migration of the energy associated with a point target takes place. If the system must also operate at a high squint angle, the azimuth signal becomes nonlinear FM. This paper describes extensions to the basic step transform algorithm that allow these imaging situations to be accommodated.