Research On Imaging And Anti-Interference Of Forward-Look Multichannel Synthetic Aperture Radar

Forward-looking synthetic aperture radar(FLSAR)is capable of reconstructing the high-resolution image of the front area.Once it was proposed,it has attracted great attention from researchers.The bistatic and multistatic FLSARs can perform high-resolution imaging processing similar to the side-view synthetic aperture radar(Synthetic Aperture Radar,SAR)imaging method,which solves the low-resolution problem of FLSAR.However,bistatic and multistatic FLSARs face many problems such as high system complexity and coordination and synchronization between platforms.Different from bistatic and multistatic FLSARs,monostatic airborne FLSAR system is famous for its small amount of equipment and simple imaging algorithms.However,the monostatic airborne FLSAR system suffers from the left/right ambiguity problem.In order to solve the left/right ambiguity,a multichannel array needs to be used for solving azimuth ambiguity.Therefore,the forward-looking multichannel SAR(FLMCSAR)system comes into being.In addition,with the upgrading of electronic countermeasures technology,various electronic devices in military applications often need to be used in a complex electromagnetic environment.Moreover,they may be attacked by the enemy's active electromagnetic interference.FLSAR systems are often on the front lines of the battlefield with complex electromagnetic environments,so researching on anti-jamming algorithm is important.In summary,this thesis focuses on the imaging and anti-jamming algorithms of the FLMCSAR system.In this thesis,theoretical derivation,simulation experiments,and raw data experiments are carried out.The main contents are as follows:1?First,the basic principles of FLMCSAR are theoretically deduced,and the basic FLMCSAR imaging and solving ambiguity algorithms are introduced.In addition,all algorithms are verified by simulated and raw data experiments.2?Secondly,due to the narrow Doppler bandwidth of the forward-looking SAR echo,a forward-looking SAR imaging system based on DD-MIMO(Doppler Diversity-Multiple Inputs Multiple Outputs,DD-MIMO)is proposed.The algorithm makes full use of the high pulse repetition frequency,realizes the expansion of receiving channels,and greatly improves the performance of solving azimuth ambiguity.3?Finally,the two types of active jamming,i.e.,active deception jamming and FM slope mismatch jamming,are deeply studied,and corresponding anti-jamming algorithms are proposed.Aiming at active deception interference,an interference identification and suppression algorithm based on space-time joint filtering is proposed.This algorithm can effectively suppress interference while ensuring that the true echo signal is complete.In addition,an orthogonal matched filtering method is proposed for FM slope mismatch interference.This algorithm reconstructs the interference signal spectrum to construct an orthogonal matched filter.The orthogonal matched filter is used to match filter with the echo signal,which can greatly suppress the interference signal while preserving the true echo signal.This algorithm is applied in the forward-looking multi-channel SAR system without losing the airspace freedom,and the performance of the solving ambiguity is guaranteed.Simulation experiments are carried out for each algorithm mentioned in this paper,and compared with other algorithm of the same kind.In addition to simulation experiments,the raw data based on the airborne FLMCSAR experimental system is also used to verify the FLMCSAR imaging algorithms and solving ambiguity algorithms.The experimental results have validated the performance of the proposed algorithms.