###### Abstract  
Synthetic aperture radar (SAR) systems are susceptible to radio frequency interference (RFI). The existence of RFI will cause serious degradation of SAR image quality and a huge risk of target misjudgment, which makes the research on RFI suppression methods receive widespread attention. Since the location of the RFI source is one of the most vital information for achieving RFI spatial filtering, this paper presents a novel location method of multiple independent RFI sources based on direction-of-arrival (DOA) estimation and the non-convex optimization algorithm. It deploys an L-shaped multi-channel array on the SAR system to receive echo signals, and utilizes the two-dimensional estimating signal parameter via rotational invariance techniques (2D-ESPRIT) algorithm to estimate the positional relationship between the RFI source and the SAR system, ultimately combines the DOA estimation results of multiple azimuth time to calculate the geographic location of RFI sources through the particle swarm optimization (PSO) algorithm. Results on simulation experiments prove the effectiveness of the proposed method. s 2021 13 1207 13061207  
or take advantage of beamforming technology to achieve spatial filtering [9; 10; 11; 12; 13]. This method mainly achieves the purpose of interference suppression by reducing the RFI signal entering the receiver. For the SAR system, taking into account the spatial characteristics of the interference signal, advanced SAR systems have the ability to adaptively adjust the antenna pattern for RFI mitigation, relying on the direction-of-arrival (DOA) of the interference signal, whose feasibility has been studied in some research [9; 10]. Thus, it is greatly essential to get an accurate location of the RFI source for implementing this approach. In the research on RFI location, the works focusing on DOA estimation were studied [7; 11; 12; 13]. Among these research studies, References [7; 11] studied the effective RFI source location methods for SAR systems. In [7], SAR images were used to record the azimuth time when the interference occurs, and on this basis, the location of RFI sources was estimated based on the scene location and the signal acquisition time. However, this method does not use the characteristics of the RFI signal and can only roughly locate the RFI. In Reference [11], a uniform linear array was designed to receive the signal, and then the multiple signal classification (MUSIC) algorithm was used for the array signal to realize a one-dimensional estimation of the direction of the RFI signal. Nevertheless, this method cannot obtain the two-dimensional angle of the RFI signal direction in the azimuth and elevation, so the two-dimensional pattern of the antenna cannot be designed based on the result to achieve RFI suppression, and the precise geographic location of the RFI source cannot be calculated. Besides, References [12; 13] researched the RFI location for synthetic aperture interferometric radiometry (SAIR). Reference [12] used the MUSIC algorithm to achieve high-precision two-dimensional RFI DOA estimation. However, first of all, this work was proposed for SAIR, and the structure of the Y-shaped array designed in [12] is quite complicated for the SAR system. It is the virtual hexagonal array composed of 931 array elements, which is not suitable for SAR systems. Secondly, the two-dimensional MUSIC algorithm needs to use spatial spectrum search to complete DOA estimation, the computational complexity of this process is very high, which will greatly increase the computational burden of the system in practical applications [14; 15]. Finally, this method only estimates the DOA of the RFI signal and does not calculate the geographic location of the RFI source, but the location information is important for detecting ground interference sources. The literature [13] is also a study on SAIR, the same as [12]. In addition, it introduces the spatial sparsity of RFI and considers that the spatial distribution of RFI sources obeys a prior Laplace probability function.