Research On High Resolution Spaceborne Sliding Spotlight SAR System Design And Imaging Processing

Spaceborne sliding spotlight synthetic aperture radar(S-SS-SAR)had realized long-term and high-resolution observation by controlling beam footprint and antenna illumination angle.Squint sliding spotlight improves the multi-angle imaging capacity with the single pass and the imaging flexibility of spaceborne SAR greatly,which could obtain more abundant target information.A large range migration will lead to blind area with the increase of center-squint angle in the fixed pulse repetition interval(PRI)system.Furthermore,the increase of squint angle and data acquisition time will bring additional bandwidth and nonlinear Doppler center,which will cause spectrum aliasing seriously.Based on the above background,this thesis focuses on the system design and signal processing methods about sliding spotlight mode.The main work completed will be described as follow.1.Firstly,a block varying PRI scheme was proposed in order to solve the problem of transmitting and receiving pulses aliasing,effective data losing and blind area arising caused by large range migration with the increase of center-squint angle in the fixed PRI system.The simulation results confirm that this scheme could avoid pulses aliasing owing to the fixed PRI,and reduce the number of false targets,systematic non-uniformity and accumulated errors owing to the continuous varying PRI.2.Secondly,the azimuth time-frequency relationship of squint sliding spotlight mode was studied in depth.The spectrum will be aliasing if the azimuth de-ramping preprocesses directly by conventional two-step algorithm.A modified azimuth preprocessing scheme based on sub-aperture segmentation was designed in order to solve the squint additional bandwidth and the nonlinear change of Doppler center frequency caused by the increase of center-squint angle and sampling time.This method eliminates the influence of additional bandwidth and nonlinear Doppler center on signal processing,which could realize the parallel processing of data and improve the sampling rate and the system operation efficiency.Simulation results show that this scheme can avoid Doppler spectrum aliasing effectively.3.Finally,an azimuth preprocessing method based on full-aperture is studied in view of the characteristics of serious range-azimuth coupling and difficult separation in high squint scene,which is different from sub-aperture algorithm.And the proposed method is verified by simulation.