Two frequency-domain algorithms Chirp Scaling (CS) with the advantage of simplification and Range Migration (RM) with the advantage of accuracy are candidates for a comparative study to the time-domain algorithm Fast Factorized Backprojection (FFBP) with reference to a UWB system are presented in this paper. The comparison is based on UWB SAR image quality measurements such as spatial resolution, Integrated Sidelobe Ratio (ISLR), Peak Sidelobe Ratio (PSLR) and processing time connected to computational cost. The simulated SAR data, which is used in this study, is based on the parameters of the airborne UWB low frequency CARABAS-II system.