Research On Multi-Aperture Spaceborne SAR System And Signal Processing For High Resolution Wide Swath Imaging

Geometric resolution and range swath are the two most important indicators of spaceborne synthetic aperture radar(SAR).However,in conventional single-channel SAR system,these two indicators cannot be improved simultaneously,due to the limitation of the minimum antenna area,making the task of earth observation with high resolution and width swath cannot be achieved.Multi-aperture SAR system is one of the most effective ways to achieve high resolution and wide swath imaging for spaceborne SAR.The multiple azimuth beam SAR and multiple elevation beam staggered SAR are the two most interesting types of multi-aperture SAR.This thesis focuses on the system design and signal processing for these two types of SAR system.The main work and innovations of the thesis are listed as follows:1.In order to solve the problem of non-uniform azimuth sampling in azimuth multi-beam SAR systems,the azimuth transmit and receive phase center adaptive joint adjustment approach is proposed.The transmit and receive phase centers are jointly adjusted to make azimuth samples uniformly distributed,and the subsequent multichannel reconstruction processing can be omitted.The approach is verified by simulation experiments on point targets.Then in order to suppress false targets caused by residual channel errors after channel error compensation,two false target suppression approaches based on the non-uniform adjustment of the receive phase centers,and based on random disturbance phases,respectively,are proposed.Simulation experiments on point targets verify both approaches.2.Since different phase center deviations are caused by different beam steering laws in azimuth multichannel beam steering SAR,the cost of different beam steering laws and the impact on imaging results are analyzed to provide a theoretical basis for the design of actual systems.Then to solve the problem of severe Doppler aliasing in multichannel sliding spotlight SAR with large pulse bandwidth and azimuth steering angle,azimuth preprocessing approaches based on range-frequency-dependent de-ramping is proposed,and the computational complexity is analyzed.Simulation experiments on point targets verifies the preprocessing approaches.3.In order to solve the problem of azimuth non-uniform sampling caused by pulse repetition interval(PRI)variation in Staggered SAR systems,a joint strategy of PRI variation and phase center adjustment is proposed.The system design process with a design example is given,and imaging performances are analyzed.In addition,the corresponding signal processing approach are dicussed according to the characteristics of the PCAS SAR echoes.Finally,the approach is verified by simulation experiments on point targets and distributed targets.