High Resolution Imaging Algorithms For Airborne Nonparallel-Track Bistatic Synthetic Aperture Radar

Bistatic synchronized aperture radar(Bi SAR)are characterized by separated platforms for the transmitter and receiver.Due to the separation of the transmitter and the receiver,the Bi SAR can configure the geometry of platforms according to the different requirements of imaging applications.Compared with the monostatic SAR systems,it offers additional benefits like anti-detecting,anti-distrubing and high viability,Bi SAR has broad application prospects.Nonparallel-Track Bistatic SAR refers to a new system of bistatic SAR with two platforms moving with the different velocity vectors.Due to the fact that the instantaneous relative position between the receiving and transmitting platforms is spatially variant,illuminance synchronization problem can't be ignored,and the signal data will be subject to characteristic of the 2-D spatial variance of the RCM,these will increase the imaging difficulty in the wide-swath and high-resolution cases.According to the characteristic of the different modes,this paper mainly focuses on the Nonparallel-Track Bistatic SAR imaging algorithm,And the main research contents are as follows:1.An extended nonlinear chirp scaling(ENLCS)algorithm based on a quadratic ellipse model with two motion platform parameters is proposed for this configuration.For range processing,a method combining linear range walk correction and keystone transform is adopted to remove linear RCM completely and mitigate range–azimuth cross coupling.For azimuth focusing,a quadratic ellipse model using the two motion platform parameters is established to depict the azimuth-variant properties of the Doppler frequency modulation(FM)rate,and its accurate high-order approximation is derived as well.Investigations of the quadratic phase error show that great improvement can be made by this model.Following which,coefficients of the ENLCS are derived to accomplish the azimuth equalization.The theoretical resolutions in both range and azimuth are 1.0m,and the squint angle of the receiver is 30° Resolution Simulation results validate the effectiveness of the algorithm proposed by this letter.2.For wide-swath highly squinted Bi SAR,an extended frequency-domain nonlinear scaling(FNLCS)algorithm is proposed based on the ellipse model with azimuth-dependent squint angle is proposed to obtain better focusing for in this paper.Firstly,to solve the illuminance un-synchronization problem,the accurate geometric configuration and signal model of the azimuth-dependent squint angle is constructed.After range processing of combining LRWC,KT transform and Bulk RCMC,a new analytical model with azimuth-dependent squint angle is proposed based on the new geometric configuration,which accurately describes the actual change process of the beam center distance of the point target and the azimuth-variant characteristics of the range offset of the point target.The derivation results of the ellipse model are applied to solve azimuth-dependent residual high-order RCMC,and the accuracy of the migration correction can be improved obviously.Then,aiming at the azimuth-dependent Doppler phase,FNLCS algorithm is proposed based on the new model to enhance the performances of azimuth equalization and compression obviously in the case of wide swath high-resolution highly squint case,which solves the azimuth-dependent Doppler centroid.Finally,Simulation results validate the effectiveness of the algorithm proposed by this letter.