This paper presents an iterative method to estimate the Normalised Relative Speed (NRS) of ground moving targets in Ultra Wideband (UWB) wide beam Synthetic Aperture Radar (SAR) using one antenna. The number of iterations depends on the separation between processed NRS and true target NRS. The NRS estimate is based on a chirp rate estimator in azimuth direction of the SAR image. The paper derives an analytical expression of the azimuth phase information based on the moving target NRS and the NRS used in the image formation. The method has been tested on real data from the CARABAS-II SAR system showing good results.