Abstract: Based on a two-step processing approach and the chirp scaling algorithm,a general high-resolution spotlight synthetic aperture sonar(SAS) model suitable for broadside imaging is presented.The model combines the advantages of the SPECAN and chirp-scaling algorithms.Azimuth coarse focusing is first achieved with deramp processing and upsampling operations,and the azimuth spectral aliasing typical of spotlight SAS is overcome.Precise range focusing is then achieved based on the chirp scaling principle.The residual azimuth phase errors are compensated for to acquire refined azimuth focusing.Using the general spotlight model,an implementation is given.The whole algorithm can be implemented by complex multiplication and FFT without any data interpolation.The algorithm is suited to wide range swath high-resolution spotlight SAS imaging.Computer simulation shows validity of the general model.