Abstract: A new range-Doppler imaging algorithm is presented for processing bistatic Synthetic Aperture Radar (SAR) data acquired in the hybrid spaceborne/airborne sliding spotlight SAR configuration. This paper firstly presents the 2-D point target spectrum by using the series reversion, and then analyses the spectrum with the space-variant in range. Based on the previous discussions, the algorithm overcomes the spectrum folding of the azimuth raw signal with a SPECtral ANalysis (SPECAN) process, and focuses the full image in the Doppler domain. Without sub-aperture and interpolation, this algorithm is great in computational efficiency. Simulation results confirm the validity of the imaging algorithm.