# Sparsity-Inducing Super-Resolution Passive Radar Imaging with Illuminators of Opportunity  
[PERSON]  
1 Research Institute of Electronic Science and Technology, University of Electronic Science and Technology of China, Chengdu 611731, China; [EMAIL_ADDRESS] (Y.Z. ); [EMAIL_ADDRESS] (W.Q.W.) Electronics and Information School, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore; [EMAIL_ADDRESS]  
[PERSON]  
1 Research Institute of Electronic Science and Technology, University of Electronic Science and Technology of China, Chengdu 611731, China; [EMAIL_ADDRESS] (Y.Z. ); [EMAIL_ADDRESS] (W.Q.W.) Electronics and Information School, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore; [EMAIL_ADDRESS]  
[PERSON]  
1 Research Institute of Electronic Science and Technology, University of Electronic Science and Technology of China, Chengdu 611731, China; [EMAIL_ADDRESS] (Y.Z. ); [EMAIL_ADDRESS] (W.Q.W.) Electronics and Information School, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore; [EMAIL_ADDRESS]  
[PERSON]  
2 Electronic and Information School, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] 2 and 2  
Several investigations have been performed for passive ISAR imaging [9; 10; 11; 12; 13]. In [9], a smoothed pseudo Wigner-Ville distribution (SPWVD) has been applied for passive ISAR cross-range processing to achieve wide-angle imaging. However, this algorithm requires a large number of illuminators to provide a large rotation angle and a large computation complexity induced by the time-frequency transform. In [10; 11], an experiment to enhance the cross-range resolution of passive ISAR image using digital TV based passive bistatic radar (PBR) has been carried out. It is demonstrated that a moderate resolution can be expected for the polar format algorithm (PFA), but there is a tradeoff between the imaging swath and the resolution. In [12; 13], a passive ISAR processing scheme is presented by exploiting the multichannel digital television broadcasting (DVB)-T signals, which is verified by the experimental results of ship and civilian aircraft imaging. Nevertheless, since the rotation angle is only several degrees, it is still difficult to obtain a meaningful passive ISAR image. Thus, a large rotation angle should be employed for the system. In general, a large rotation angle means a long observation time. However, when the target is maneuvering, the target may not be irradiated by the IO and passive radar simultaneously, which makes long-term data collection very difficult. Moreover, portions of the data may be missed due to uncooperative IO. To resolve these problems, effective algorithms should be developed for passive ISAR super-resolution imaging, particularly for the cases with a small rotation angle as well as with limited measurements. In [14], an ESPRIT based super-resolution imaging algorithm based on external illuminators is proposed under the condition of small angular rotation, where ESPRIT [15] is used to estimate the spatial frequencies of different scatterers on the target. RELAX [16; 17] can also estimate the amplitude and frequency of multi-component complex sinusoidal signals and has been successfully applied for super-resolution SAR imaging. Although the proposed scheme seems to work well for super-resolution passive radar imaging, we should be aware that both ESPRIT and RELAX are more or less sensitive to noise and modeling errors. In addition, applying ESPRIT or RELAX for passive radar imaging will require a considerable amount of measurements and, consequently, it is impractical for actual applications.