Bistatic FDA 3D-SAR Imaging Technology Research

Different from the characteristics of single-base SAR(Synthetic Aperture Radar,SAR)that can only obtain the scattered information of the target in one direction,the bistatic SAR has the advantages of long range,richer information and strong security,so it can be widely used in the military and civilian fields.In the field of imaging,the combination of bistatic SAR and linear array antenna can complete the three-dimensional imaging of the target scene,and its system principle is the same as that of the traditional SAR threedimensional imaging,through the antenna erection platform and the target relative motion synthesis of two-dimensional virtual area array,combined with pulse compression technology,to achieve three-dimensional information resolution of space targets.However,this wideband signal-based imaging mechanism makes it difficult to separate the signals at the receiving end and increases the complexity of the system hardware.Therefore,this paper introduces a Frequency Diversity Array(FDA),using its "swap space for bandwidth" feature,combined with bistatic SAR,to propose a new three-dimensional imaging system-bistatic FDA three-dimensional SAR imaging system.The system synthesizes the broadband detection performance through the transmission mode of narrowband signals,breaking through the limitations of hardware replication and echo signal separation of traditional bistatic SAR transceivers.Based on the existing single-base SAR imaging model and combined with the characteristics of FDA,this paper studies high-precision three-dimensional imaging scheme of the bistatic FDA three-dimensional SAR.The main research work is as follows:1.The theoretical basis of bistatic SAR and FDA is introduced.Firstly,the model categories of bistatic SAR,the imaging models and principles under the general configuration are given,including the geometric model and echo model of the bistatic SAR system;secondly,the beam characteristics,beam resolution and two types of reception mechanisms are studied on the basis of the linear array structure of the frequency diversity array;finally,two sparse arrays,the coprime array and the nested array,are introduced to lay the foundation for system optimization.2.A model of the bistatic FDA three-dimensional SAR imaging system is established,and the imaging algorithm of bistatic FDA three-dimensional SAR is proposed.First of all,the oblique distance process formed by the transceiver separation of bistatic SAR is more complicated,which brings certain difficulties to signal processing and algorithm research,proposes the principle of equivalent array elements,and verifies the principle from the two aspects of theoretical derivation and beamforming;secondly,on the basis of the above theoretical basis,the geometric model,echo model and the 3D resolution of full frequency receive(FFR)mechanism of the bistatic FDA three-dimensional SAR system are constructed;then the traditional Backward Projection algorithm with a wide range of applications is improved to complete the 3D imaging simulation,which verifies the effectiveness of the improved algorithm and the feasibility of the new imaging system;in view of the sparse characteristics of the time domain and airspace of the echo signal,the emerging Compressed Sensing(CS)theory is used to study the compression perception 3D imaging algorithm based on the OMP reconstruction in the greedy tracking algorithm to improve the quality of images.Finally,the comparison analysis of the imaging performance of the two algorithms is derived.3.Optimization of the initial bistatic FDA three-dimensional SAR imaging system is completed.Aiming at the defects of the bistatic FDA three-dimensional SAR imaging system under FFR that requires a wide range of signal frequencies covered by the receiving end,a large amount of system data processing,and a high difficulty in implementing the system hardware,the system optimization of the bistatic FDA three-dimensional SAR imaging scheme based on Single Frequency Receive(SFR)is studied.However,due to the synchronous change of the phase synchronization caused by linear frequency offset and uniform array spacing,there is a range-angle coupling phenomenon in the FDA beam.Conventional linear frequency increments and uniform arrays combined with the SFR mechanism cannot achieve 3D imaging.Therefore,from the perspective of breaking the linear change of frequency increment,three typical forms of nonlinear frequency increment,logarithmic form,square form and random form are proposed,and the beam focusing ability is compared and analyzed;the virtual array antenna along the track and the actual array up the cut trajectory are studied by using SFR bistatic FDA three-dimensional SAR imaging under the full stochastic scheme of random frequency increment.and SFR bistatic FDA three-dimensional SAR imaging in a semi-random scheme that uses only random frequency increments on the actual antenna array and constant frequency increments on virtual synthetic aperture arrays.Finally,from the perspective of breaking the uniform spacing of the array elements,two typical sparse arrays,coprime arrays and nested arrays are introduced,and the SFR bistatic FDA three-dimensional SAR imaging based on these two arrays is studied.