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

Bistatic synthetic aperture radar(Bi SAR)with the receiver and the transmitter located on different platforms is a new type of radar.Compared to the monostatic SAR,the imaging mode for Bi SAR is more complicated and varied,and its system configuration is also more flexible.Due to the high safety performance,excellent information acquisition ability and strong anti-interference ability,Bi SAR has been widely concerned and applied to military and civil fields.However,due to the feature of transceiver separation,the beam synchronization,frequency synchronization,and time synchronization as well as challenges such as diversification of imaging mode,limitation of imaging algorithms,and complexity of data modeling have to be considered for Bi SAR.The key contents for this paper are listed as follows:1.For highly squinted and high-resolution Nonparallel-Track Bi SAR,the beam nonsynchronization results in an azimuth-dependent range offset,which makes the spatial variance of range cell migration(RCM)and Doppler parameters become more serious.To accommodate these issues,a new imaging mode where receiver's beam follows the transmitter's one actively by adjusting the squint angle of receiver is proposed,and a modified quadratic ellipse model with the azimuth-variant receiving squint angle is constructed to reveal the azimuth-variant property of the azimuth distributed targets more precisely.2.In the case of the innovative imaging mode,an improved frequency extended nonlinear chirp scaling(FENLCS)algorithm integrated with a modified quadratic ellipse model is developed.Firstly,a linear range walk correction(LRWC)is utilized to remove the range-azimuth coupling mostly.And a KT(keystone Transform)is applied to correct the residual linear RCM of azimuth-central point targets completely,and a Bulk range cell migration correction(RCMC)is carried out to compensate the invariant part of high-order RCM.However,the residual high-order RCM originated from the azimuth-variance of NPBi SAR still exists and cannot be overlooked,especially in the condition of the varying squint angle of receiver,which will brings about a great degradation to imaging quality.Besides,the spatial variance of Doppler parameters becomes more complicated due to the involvement of Doppler centroid left by the reference LRWC.3.According to the range preprocessing,based on this innovative model,some innovative improvements on image formation are made.An ADH-RCMC is performed by which the residual azimuth-dependent high-order RCMs are corrected.More importantly,an improved FENLCS that takes highly varying Doppler centroid into consideration is re-derived to accomplish the equalization for Doppler parameters.The final high-resolution focusing is fulfilled in the range-azimuth time domains using compensation functions,and well-focused NPBi SAR images are produced.Simulation results validate that the proposed configuration and algorithm are capable of achieving the high-resolution and large-region NP-Bi SAR data focusing.