Research On The Key Techniques Of Multi-Channel High-Resolution And Wide-Swath SAR Imaging

Synthetic Aperture Radar（SAR）is a radar technology that has high-resolution images of a target area.This technology is extensively employed in both military and civilian domains for a range of applications.High resolution and wide swath（HRWS）have become an inevitable requirement for SAR system design.However,conventional SAR technology faces inherent limitations in achieving high-resolution imaging along with wide swath coverage,primarily due to constraints arising from the minimum antenna area.In order to solve the contradiction of HRWS,azimuth multi-channel SAR system compensates for the deficiency of time sampling by spatial sampling,achieving the requirement of high resolution and wide swath.In new radar systems such as multi-channel SAR and MIMO SAR,the echo data needs to be preprocessed before imaging processing.Therefore,thesis focuses on the key technology of azimuth multi-channel SAR imaging and conducts research on the following specific contents:（1）Present an overview of the current research status and theoretical basis of the thesis.Specifically,it briefly outlines the research background and emphasizes the significance of the study.Then,it elaborates on the relevant theoretical knowledge of HRWS SAR,including SAR technology,minimum antenna area,imaging algorithms,etc.It also establishes ideal and error-containing multi-channel SAR signal models respectively,laying a theoretical foundation for the key technology of data preprocessing in subsequent research.（2）Describe the research on azimuth signal reconstruction algorithm based on periodic non-uniform sampling and its computational complexity reduction to address the problem of Doppler ambiguity caused by non-uniform distribution of equivalent phase centers in multi-channel SAR system.According to the distribution of the equivalent phase center along the track,the multi-channel SAR system can be regarded as a periodic non-uniform sampling in the azimuth direction.By using the relationship between the non-uniform signal spectrum and the original analog signal spectrum,the Doppler spectrum of the multi-channel SAR without ambiguity is reconstructed,and the utilization of NUFFT and Kumar algorithm has led to a reduction in the computational complexity of the algorithm.Finally,through the reconstruction of sinusoidal signal and LFM signal with non-uniform sampling and the experiment of 2D imaging with simulation data and measured data,it can be seen that the proposed algorithm can realize the reconstruction of non-uniform sampling signal and can effectively suppress the azimuth ambiguity.（3）Discuss a study on baseline error correction algorithm based on maximum average power ratio to address the problem of azimuth pulse compression main lobe energy leakage caused by baseline errors in multi-channel SAR systems.Traditional correction algorithms often ignore the influence of baseline errors,but the SAR error model shows that the phase corresponding to baseline errors is related to the Doppler frequency,and the detection of moving targets in multi-channel SAR is related to the azimuth baseline.Therefore,it is necessary to study the estimation and compensation of baseline errors.Simulation results show that as the baseline error increases,the energy of the azimuth compressed main lobe leaks into the sidelobes,resulting in degraded image quality.The algorithm estimates errors in the baseline by optimizing the average power ratio and corrects phase errors caused by baseline errors.The experiment shows that the accuracy of baseline error estimation reaches10^-4after five iterations.In conclusion,the proposed algorithm can effectively estimate baseline errors and achieve high-quality images after phase compensation.