Study On ISAR Imaging Of Space Targets Using BP Technology

Inverse synthetic aperture radar(ISAR)is a kind of high-resolution imaging radar for non-cooperative targets,which has advantages in both military and civil fields.In recent years,with the development of space resources exploration,space detection and defense become more and more important.Space target imaging using ISAR technology has become one of the important research focuses of space detection in recent years.Radar can track the trajectory of the space targets,and certainly the space targets can be regarded as the cooperative target.As a result,the space targets can be imaged by Backprojection(BP),which can get the higher resolution under the large angle.This thesis talks about ISAR imaging method based on BP,the corresponding motion error analysis,the autofocus method and velocity compensation technique with the high-speed targets.Firstly,the thesis briefly elaborates the principle of ISAR imaging,introduces the research status of ISAR imaging technology for space targets simply,and presents the research background in this thesis and main contents.Secondly,the ISAR imaging technology based on BP is described in detail,including the idea and realization of BP imaging.By comparing the imaging results of BP with them of RD,this section analyzes and verifies the performance of BP method.The results show that the BP imaging has higher resolution than the RD when the trajectory of space targets can be tracked accurately.In particular,the BP algorithm avoids Motion Through Resolution cell(MTRC)under the large angle,when compared with the RD algorithm.Thirdly,due to the limitation of the accuracy of trajectory tracked by the radar,there are motion errors in the target trajectory.The error will result in uncorrected reconstruction images inevitably.The thesis gives the detailed analysis of the positioning errors in ISAR imaging of space targets due to motion errors of the targets,and presents an explicit quantitative relationship between the motion errors of the targets and the position errors in the reconstructed image.The effect of motion errors on the imaging is analyzed for several specific trajectory error models.Then,the simulation results validates that the analysis above is correct.Then,in order to eliminate the imaging errors caused by trajectory errors,the thesis presents the BP autofocus approach based on maximizing image sharpness.Unlike the traditional method,this algorithm uses a coordinate descent framework to focus a standard BP image with respect to all pulses.It converts the problem of seeking multiple solutions to seeking single solution,which simplifies the process of phase estimation.The feasibility of the proposed algorithm is verified by simulations,and it is applicable to arbitrary error models.Next,the thesis studies the intra-pulse compensation technique of high-speed targets,which includes the frequency modulation rate estimation based on fractional Fourier transform and the velocity estimation based on minimum entropy,both of which can compensate the speed on the basis of high-speed model.The former is applied to the de-skewed echo signal,while the latter applies to the original echo signal.Then,the performance of the algorithm is verified by the simulation experiments.At the end,the work of the whole thesis is concluded.The issues to be studied next are pointed out.