For bistatic spotlight synthetic aperture radar (SAR) with parallel trajectory, this paper investigates a fast back-projection (BP) imaging algorithm based on spectrum compression. The long synthetic aperture is split into several short subapertures (SAs), and each of them constructs a SA image with coarse azimuth resolution in a unified rectangular coordinate system by BP integral. Then, by applying the spectrum compression technique introduced in the paper, the azimuth spectrum of the SA image can be compressed greatly and, as such, the images can be coherently accumulated after azimuth up-sampling and spectrum recovery. Since there is no need for data interpolation in the image fusion, the proposed algorithm can achieve high precision as the original BP algorithm does but with higher computational efficiency. Simulation experiments are presented to validate the effectiveness of the method.
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