I. Introduction
Synthetic aperture radar (SAR) has many uses in both military and civil applications because of its capabilities of high resolution, remote sensing, and near independence from all weather conditions [1]. However, the radio signal coexists as an interference with the SAR, and it returns to deteriorate image quality if it goes untreated. In particular, in military applications, radio frequency interference (RFI) is occasionally utilized to perform destructive interference to SAR systems. Therefore, effective interference suppression methods are desired to enhance image quality and attract considerable research interest in the SAR community [2]. RFI occasionally consists of intentional/unintentional interferences coming from networks, communication systems, and other sources. According to the radio management regulations, the bandwidth of the RFI signal is substantially less than that of the transmitted signal of SAR. Thus, RFI can be treated as a narrow-band signal compared with the bandwidth of SAR systems. Based on this narrow-band property, the interference can be approximately represented by the superposition of multiple sinusoids [3].