The polar format algorithm (PFA) for the bistatic spotlight-mode synthetic aperture radar (SAR) imaging is based on the planar wavefront assumption. As the unrealistic planar wavefront assumption introduces phase error terms in the focusing process

there will be space-variant geometry distortion and defocusing effect in the image focused via bistatic PFA. Hence

the focused scene size when using bistatic PFA is usually restricted severely to avoid the defocusing effect. Based on the expansion of the received signal’s phase term in bistatic SAR

the analytical expression of the wavefront curvature error in bistatic PFA is derived in our study. Based on the expression

the space-variant filtering and interpolation operation are applied to compensate for the defocusing effect and correct the geometry distortion in the image

respectively

which extends the focused scene size of bistatic PFA effectively. Point target simulation validates the algorithm.