Abstract: Stepped chirp radars achieve high range resolution through bandwidth synthesis. Precise beginning sampling range is a significant factor which guarantees the performance of bandwidth synthesis. The effect of the beginning sampling range error on bandwidth synthesis is discussed by the way of impulse response of linear system. The beginning sampling range error introduces step phase errors which remain in the synthesized broad band pulses and result in grating lobes in the compression results. The effects on the envelope, height and distribution of the grating lobes and the shift of the main lobe are analyzed quantitatively.