Research On Signal Processing Technique For Bistatic Forward-looking SAR With Complicated Motion

Bistatic synthetic aperture radar(Bistatic SAR,Bi SAR)is a new type of SAR imaging system that separates the transmitting station and receiving station on different platforms.Compared with the traditional monostatic SAR,its system configuration is more flexible.It has many advantages such as obtaining more information from multi-directional scattering and that the receiver works in silence.What is more,it can realize high-resolution imaging in the forward-looking area of the receiver.Therefore,it has significant application value in many fields of both military and civil.Bistatic forward-looking SAR(BFSAR)under complicated motion is a special Bi SAR application mode,where the transmitter and the receiver are mounted on platforms whose trajectories include unignorable high-order components and are not completely the same.The study of this mode is not only conducive to improve the adaptability of bistatic SAR imaging technology to the non-ideal motion of the practical platforms,but also promote the application of BFSAR imaging to more complicated motion platforms such as high-speed aircraft.The realization of BFSAR imaging under complicated motion needs to solve some key technical problems such as echo signal modeling and system characteristic analysis,problem of azimuth ambiguity and highly efficient and highly accurate imaging method.This paper analyzes and demonstrates these problems in detail,and puts forward the corresponding technical methods,including the following contents:1.The range and echo models of BFSAR under complicated motion are established.The basic characteristics of each domain,echo range migration,phase modulation and space variation characteristics of echo signal are analyzed.The differences between BFSAR under linear and complicated motion and their main influence on imaging realization are summarized;2.Based on the relationship between SAR wavenumber spectrum and spatial resolution performance,a widely applicable two-dimensional resolution formula is proposed,which solves the limitation of insufficient accuracy of the traditional Bi SAR resolution formula under complicated motion and provides a more reliable prediction of the resolution performance and also principle of parameter designing;3.A general-duty prediction equation for the positions of grating lobes of Bi SAR is derived,and the differences between traditional azimuth spectrum aliasing and the azimuth grating lobes are demonstrated.Based on it,a more reasonable principle of designing the azimuth sample rate for BFSAR under complicated motion is provided..4.A highly accurate imaging algorithm for BFSAR under complicated motion based on accurate wavefront curvature correction for Polar Format Algorithm are proposed.The problem of the space-variation of echo signal under finite and infinite order of platform trajectories,respectively,is solved through two different approaches to obtain the correction filter,which realizes highly accurate and efficient imaging processing for large imaging scenes.5.Two imaging algorithms based on low-complexity space-variant filtering through uniform decoupling are proposed.They realize the decoupling with different level of resolution or space-variation through a proposed coupled-wavenumber transform and through Keystone transform,respectively,and hence realize accurate and highly efficient imaging processing for large imaging scene.The above theoretical analysis and methods are verified by simulation calculation or actual test,and the verification results prove the correctness of the above analysis conclusion and the effectiveness of the technical method.