Study On Imaging Algorithm Of Airborne Squint Bistatic Synthetic Aperture Radar

The airborne squint Bistatic Synthetic Aperture Radar(BiSAR)has flexible configuration where the transmitter and receiver are carried on different platforms.Due to the flexible configuration,BiSAR can obtain abundant scattering information with enhanced anti-interference capability during imaging.However,the flexible geometrical configuration also leads to strong range space-variant property and azimuth space-variant property,those make SAR imaging more complicated,conventional SAR technology can hardly meet these requirements.On account of the characters of airborne squint BiSAR,Imaging Algorithm of Airborne Squint BiSAR is studied in this dissertation based on azimuth-invariant and azimuth-variant these two different kind of geometrical configuration.The main works and innovations of this dissertation are given as follows.In comparison with conventional SAR,azimuth-invariant BiSAR is easier to deploy and safer,while the imaging algorithm getting more difficult.The azimuth-invariant BiSAR geometrical configuration made the property of Range Cell Migration(RCM)more complex than traditional SAR,which is no longer the linear dependence of range.Another point is range-variant Secondary Range Compression(SRC).In order to solve these issues,an improved Nonlinear Chirp Scaling(NLCS)algorithm is proposed to deal with the airborne azimuth-invariant BiSAR imaging.RCM of azimuth-invariant BiSAR is deeply analyzed in this dissertation first.Then an NLCS algorithm is improved to eliminate the range-invariant property of SRC and second order component in RCM.An improved NLCS function is used to overcome the range fading and get a better focused image.Finally,the secondary CS is employed to obtain the actual position of object.The improved algorithm without interpolation has small computation and high efficiency.Simulation results show that the improved NLCS algorithm enhances the focusing performance of azimuth-invariant BiSAR imaging compared with the conventional one.The relative position between transmitter and receiver in azimuth-variant BiSAR change with azimuth time results in azimuth-variant Doppler frequency modulation rate,furthermore,different motion vectors between transmitter and receiver leads to different Doppler frequency modulation properties of the same target,these properties brings about problems for bulk processing of targets in imaging scene area.These problems not only leads to low performance of focusing processing but also bad for real-time imaging,not to mention bulk processing precisely and efficiently.To accommodate for the problems in azimuth-variant BiSAR,an azimuth-variant algorithm is proposed for airborne BiSAR imaging based on eclipse model.the azimuth-variant property is deeply investigated first.Then an eclipse model is proposed to describe the azimuth-variant property of azimuth-variant BiSAR effectively.Based on this model,an imaging algorithm for azimuth-variant BiSAR is derived.Simulation results show that proposed model not only reveals the property of azimuth-variant in BiSAR,but also provides a precise analytical expression to depict the azimuth space-variant property of BiSAR,furthermore,the proposed algorithm for azimuth-variant BiSAR based eclipse model has higher imaging performance than conventional algorithm.