A fast implementation of the convolution backprojection (CBP) algorithm in spotl ight synthetic aperture radar (SAR) is presented based on the fast Fourier transform(FFT). Traditionally

the computation of the ′backprojection′ process is expensive

since resampling in t he process is implemented by using the interpolation operation. By analyzing the relative location relationship among different pixels

the algorithm realizes the ′backprojection′ using a series of FFTs instead of the interpola tion operation. The po int target simulation validates that the new algorithm acce lerates the CBP algorithm

and the computational rate increases about 85％.