Study On High-resolution Inverse Synthetic Aperture Radar Imaging Of Multiple Targets

High-resolution inverse synthetic aperture radar(ISAR)imaging could acquire rich structural and motion information of the observed targets,thereby providing powerful technical support for target classification and recognition,and playing a vital role in space situational awareness and ballistic missile defense.For single stationary target,well-focused image can be obtained by the conventional range-Doppler(RD)algorithm after motion compensation.In practical applications,however,ISAR is often confronted with complex multi-target observing environments,which will bring great difficulty for focused imaging.When there are multiple targets within the same radar beam(such as aircraft in a formation,multiple ballistic targets,etc.),the echo overlaps with one another in the range-slow-time domain due to the similar motion of the sub-targets.At this point,conventional motion compensation and imaging methods for single target will fail,increasing the difficulty of precise imaging of multiple targets.When there are multiple targets within multiple radar observing beams,how to allocate the limited radar resources reasonably among the imaging tasks according to target characteristics and prior information of the environment has become the key issue to the efficiency improvement of high-resolution ISAR imaging systems.Due to the complexity of multi-target observing environments,there still remain many problems to be solved at present.In this thesis,techniques for high-resolution ISAR imaging of multiple targets are emphatically studied from three aspects,i.e.high-resolution ISAR imaging of multiple rigid-body targets based on range-profile separation,high-resolution ISAR imaging of multiple micro-motion targets based on time-frequency analysis,and radar resource scheduling among multiple micro-motion targets based on high-resolution imaging.The first two aspects focus on imaging of multiple targets within the same beam,while the last aspect focuses on multi-target imaging within multiple beams.The related work will provide theoretical and technical support for improving multi-target sensing and detecting capabilities of imaging radars in China.The main content of this thesis is summarized as follows.In the first part,high-resolution ISAR imaging methods of multiple rigid-body targets based on range-profile separation is studied.Firstly,the imaging model of multiple rigid-body targets with uniformly accelerated rectilinear motions is established.Then,to give reference for ISAR waveform selection under complex environments,high resolution range-profile synthesis methods of three typical frequency modulated waveforms,namely linear frequency modulated waveforms,stepped frequency waveforms,and chirp stepped frequency waveforms,are studied respectively,and their advantages and disadvantages are analyzed.On this basis,for multiple targets with second-order translational motion,a high-resolution ISAR imaging method based on Hough transform is proposed.Furthermore,for multiple targets with third-order translational motion,a high-resolution ISAR imaging method based on particle swarm optimization is proposed.Finally,the effectiveness of the proposed methods is validated by experimental results of simulated data.In the second part,high-resolution ISAR imaging of multiple micro-motion targets based on alternating direction method of multipliers(ADMM)is studied.Firstly,the motion models of multiple micro-motion targets are established,which include the general micro-motion model and motion models of three typical micro-motions,i.e.spinning,precession,and nutation.To solve the issues arising from random defect in the cross-range direction,a rangeinstantaneous-Doppler(RID)imaging method based on ADMM is proposed for multiple micro-motion targets.Finally,the effectiveness of the proposed method is validated by experimental results of simulated data.In the third part,ISAR resource scheduling method for multiple micro-motion targets based on ADMM-based high-resolution imaging is studied.Firstly,according to the characteristics of the ADMM-based time-frequency reconstruction method,the information of each micromotion target,and the prior of the environment,the requirement for radar resources and the integrated priority of each imaging task are calculated.Then,based on pulse-interleaving technology,radar resource scheduling model among multiple micro-motion targets is constructed under the dual constraints of time and energy.Aiming at the difficulty in finding analytical solution to the aforementioned model and the low stability of the existing numerical optimization methods,a radar resource scheduling method for multiple micromotion targets based on genetic algorithm is proposed.Finally,the effectiveness of the proposed method is validated by experimental results of simulated data.