Autofocus allows us to generate images with better quality by automatically adjusting the image focusing parameters. For radar imaging, autofocus means to automatically correct phase errors based on collected radar returns from targets. Inverse synthetic aperture radar (ISAR) motion compensation includes range alignment and phase adjustment. The phase adjustment process is for removing the residual translation error on phase terms. The phase errors are the causes of image defocusing. If a phase adjustment algorithm is based solely on the radar data itself, this is called the autofocus algorithm.ISAR autofocus methods can be parametric and nonparametric. Parametric method uses a parametric model of the radar-received signal. Image contrast-based autofocus (ICBA) and entropy-based autofocus algorithm belong to the parametric method . The prominent point processing (PPP) algorithm and the phase gradient autofocus (PGA) algorithm belong to the nonparametric ISAR autofocus method .