A Research On Spatial Interference Suppression Algorithms And Implementation Of FPGA

Electronic warfare aircraft is an indispensable weapon in modern warfare,but it lacks certain defense and early warning capabilities.It is very easy to face enemy missile threats in the battlefield environment.It is easy to add early warning systems through its own set of transceiver antennas.However,in the early warning system,the transmitting system and the receiving system work simultaneously,and the transmitting antenna and the receiving antenna are only 10 meters apart,and a part of the transmitted signal is directly coupled to the receiving antenna to form direct wave interference.Compared with the target echo signal,the direct wave intensity is extremely large,which seriously affects the signal-to-noise ratio,and directly causes the radar matching filter algorithm can not obtain correct results.Aiming at the direct wave interference in this system,this thesis studied a power-inversion algorithm of space-time two-dimensional structure and completed the FPGA(Field Programmable Gate Array)implementation.The specific study is divided into four parts:1)Introduced the basis of the spatial domain filtering.Aiming at the characteristics of array antennas in radar systems,the array receiving models of narrowband and wideband signals are introduced.The common spatial filtering algorithms are given: The Minimum Variance Distortion Less Response(MVDR)algorithm and the Power Inversion(PI)algorithm,which can effectively filter out some spatial interference signals.It also introduced two performance metrics for evaluating anti-interference algorithms.2)Aiming at the shortcomings of spatial filtering,the space-time adaptive(STAP)interference suppression algorithm is studied.Firstly,the Power Inversion algorithm is extended to space-time two-dimensional structure by adding time-domain taps.Then,the Wiener filter structure of the space-time two-dimensional power inversion algorithm is derived and the optimal weight expression is obtained.At the same time,the adaptive weighting algorithm commonly used in hardware systems is introduced: Sampling Matrix Inversion(SMI)and Least Mean Square(LMS),and simulation comparison is carried out.The algorithm of different tap length and different delay interval is analyzed.3)The FPGA system implementation of the direct wave interference suppression algorithm is completed.The algorithm is based on the space-time structure PI algorithm introduced in Chapter 3.Considering the design complexity and system operation rate requirements,the improved algorithm DLMS of LMS algorithm is used to calculate the weight.The hardware platform design of FPGA system is introduced.The whole signal processing flow is designed and implemented in EP5CEFA9F23I7 chip,including sampling data synchronization,band pass filtering,Hilbert transform,DLMS algorithm,and the correctness of each module is verified by simulation.4)The test of the direct wave interference suppression system is completed.The test platform is briefly introduced,and the matching filtering results before and after interference suppression are given to verify the effectiveness of the system.