Reconstruction algorithms for monostatic synthetic aperture radar (SAR) with poor antenna directivity traversing straight and arbitrary flight trajectories have been developed by various authors 1-5 , while, to our knowledge, the acquisition geometry of bistatic SAR studies for the case of poor antenna directivity are limited to isotropic antennas traversing certain flight trajectories (straight 6, 7 or circular 8, 9 flight trajectories) over flat topography.In this paper, we present an approximate analytic inversion method for bistatic SAR (Bi-SAR). 10 In particular, we present a new filtered-backprojection (FBP) type Bi-SAR inversion method for arbitrary, but known, flight trajectories over non-flat, but known, topography. These FBP type reconstruction methods have the advantage that they produce images that have the edges of the scene at the correct location, orientation and strength. We demonstrate the performance of the new method via numerical simulations.