Motion Compensation For W-Band Radar's High-resolution ISAR Targets

Inverse Synthetic Aperture Radar(ISAR)is a kind of imaging system which can detect non-cooperative targets and obtain target Radar images by means of signal processing.It is one of the important means of reconnaissance and strike in the field of space,air and ocean in China.Existing ISAR imaging system has many problems,and the movement form of the target and the target's space environment is becoming more and more complex,and the upgrading of radar equipment also promotes the development of imaging radar towards the direction of large bandwidth and high wave band,and traditional imaging algorithms is difficult to meet the needs of high-resolution imaging of the target and precise motion compensation under different motion forms of the target.Compared with the traditional band,W-band ISAR provides the possibility of target high-resolution imaging in hardware by means of the large bandwidth and high carrier frequency of W-band radar.However,there are still problems in W-band imaging,such as motion compensation and imaging,which need to be solved urgently.Firstly,ISAR high-resolution imaging technology,such as large bandwidth generation,is becoming more and more mature,which makes radar high-resolution imaging possible.At the same time,the improvement of resolution will cause obvious range migration problem,which makes it difficult for traditional algorithms to deal with the high-resolution imaging problem.Secondly,the development trend of ISAR imaging radar in the future is that the radar signal frequency is moving towards the high frequency band.Imaging radar will be more sensitive to the influence of phase noise caused by the system or environment and other nonlinear errors in the process of processing,which will reduce the image quality of ISAR radar.Finally,when ISAR is used to observe distant non-cooperative targets,the signal-to-noise ratio received by the radar system is low,and the traditional ISAR imaging algorithm is difficult to adapt to the target motion compensation and imaging under the condition of low signal-to-noise ratio.From the perspective of engineering application of W-band ISAR imaging,this paper studies the motion compensation of W-band ISAR target,introduces the main process of W-band ISAR target imaging,studies the method of motion compensation of target based on echo signal characteristics and imaging results,and makes necessary preparations for radar high-resolution imaging.The content of the thesis includes: translational compensation method under the condition of low signal-to-noise ratio of W-band ISAR,speed estimation method of W-band ISAR,imaging method of W-band ISAR for uniformly rotating target in ISAR and so on.The main content of the paper is as follows:In the second chapter,the basic principle of ISAR imaging--Range Doppler(RD)principle,imaging resolution,processing steps and corresponding algorithms of traditional ISAR imaging methods,and the technical characteristics of W-band are summarized,which establishes the theoretical basis for the subsequent research.The third part of the second chapter introduces the principle and method of motion compensation of ISAR.The fourth part of the second chapter introduces the technical characteristics of W-band and analyzes the possible motion compensation problems in the imaging process of W-band radar.The third chapter studies the translation compensation problem of W-band ISAR under the condition of low signal-to-noise and strong noise compensation problem of low accuracy.The third and fourth parts of the third chapter introduce and analyze the basic fruit fly optimization algorithm and its defects.Combining with the rough estimation method of target translation,the fifth part of the third chapter proposes a translational compensation algorithm based on an improved fruit fly optimization algorithm to accurately estimate and compensate the translational components.The algorithm consists of two steps.In the first step,the rough estimation based on target translation is carried out to provide initial values for the subsequent precision estimation of the fruit fly optimization algorithm and improve the convergence speed of the precision estimation algorithm.In the second step,after combining the chaos theory and the variable step method to improve the defects of the basic fruit fly optimization algorithm,the improved fruit fly optimization algorithm is used to estimate the translational components,which will lay the foundation for the subsequent rotation parameter estimation and rotation imaging.The translational compensation processing result of W-band simulation data proves the effectiveness of the proposed algorithm.In the fourth chapter,on the basis of the precise translational compensation in the third chapter,the rotation compensation and imaging problems of the W-band ISAR uniformly rotating target in space are studied.The second part of the fourth chapter analyzes the Migration Through Resolution Cell(MTRC)problem caused by rotation and the necessity of the correction of the MTRC.The third part of the fourth chapter analyzes the basic principle of Polar Format Algorithm(PFA)for rotation compensation and the necessity of estimating target rotation angle/speed information.The fourth part of the fourth chapter analyzes the feasibility of using the golden section method to search the target speed information based on the target translation compensation and the image minimum entropy criterion.The target speed information estimation and imaging processing results of the simulation data prove the effectiveness of the proposed method,and the W-band ISAR image quality of the PFA algorithm imaging processing is further optimized using the block-wise phase gradient autofocusing method.The block-wise phase gradient autofocusing method is introduced in the fifth part of the fourth chapter.