The paper shows an investigation of the availability of the fast time-domain algorithms to process data collected by synthetic aperture radar systems with circular apertures (CSAR). In the investigation, the reconstruction of CSAR images from data is suggested to be in a ground plane instead of a slant-range plane. The Fast Backprojection (FBP) algorithms are considered to examine the availability of time-domain algorithms for CSAR data processing. However, the availability is also applied to the Fast Factorized Backprojection (FFBP) algorithms. The simulated CSAR data with respect to the CARABAS-II parameters is used.