Analysis Of Electromagnetic Scattering Model And Imaging Method For ISAR Targets

Inverse Synthetic Aperture Radar(ISAR),which can observe and image targets all day,all weather and long distance,has the characteristics of strong anti-jamming ability and good penetration,and has been widely used in military and civil fields.ISAR imaging is a process of reconstructing and inversing the structure and electromagnetic scattering characteristics of the target.Through two-dimensional and three-dimensional high-resolution imaging of the target,abundant feature information such as geometric structure and physical properties of the observed target can be obtained.However,with the development of ISAR imaging technology and the increasing complexity of observation scenes,the discontinuous observation of targets by radar will result in the missing of echo data in some frequency bands or angles,which makes it difficult for traditional two-dimensional imaging methods to obtain well-focused images.Most of the existing attribute scattering center models are aimed at two-dimensional observation scenes and can not represent the electromagnetic dispersion of the observed targets in three-dimensional attitude.The scattering center model of target attributes in three-dimensional space is urgently needed to provide support for target feature extraction and structure reconstruction.Therefore,in this paper,the electromagnetic scattering model of ISAR target and two-dimensional and three-dimensional imaging methods are studied.The main work of this paper is as follows:1.The basic principle of ISAR imaging is introduced.Combining with the equivalent turntable model,this paper expounds the causes of the translational component of the target,introduces the methods of translational compensation in detail,analyses the electromagnetic scattering mechanism of the target in microwave frequency band,discusses the electromagnetic scattering phenomena such as mirror reflection,diffraction and cavity scattering,and gives several typical parametric characterization models of electromagnetic scattering characteristics.2.Aiming at the difficulty of focusing ISAR imaging results caused by two-dimensional sparse echo data in frequency band and angle,combined with two-dimensional attribute scattering center model,the ISAR sparse frequency band and angle observation model for target is constructed,and the selection method of observation matrix is discussed.The method of estimating parameters of target scattering center based on compressed sensing theory and two-dimensional ISAR imaging method are proposed.The simulation results verify the effectiveness of the proposed method.Secondly,aiming at the problem that the two-dimensional attributed scattering center model has limited ability to characterize the three-dimensional electromagnetic scattering characteristics of ISAR targets,the three-dimensional attributed scattering center model of single-matrix system is constructed by analyzing the three-dimensional electromagnetic scattering model of double-matrix system.Combining with six basic scatterers of flat plate,dihedral angle,trihedral angle,cylinder,cap and sphere,their scattering Center modes are deduced.The validity of the single-base three-dimensional attribute scattering center model constructed in this paper is verified by comparing the electromagnetic calculation data with the theoretical results.3.Aiming at the difficulty of track association in three-dimensional reconstruction of targets based on sequential ISAR images,the signal model of sequential ISAR imaging is constructed,and the analytical form of three-dimensional structure of scattering center on target to two-dimensional imaging plane is deduced in detail.Through the analysis of its motion characteristics,the track association of scattering center is modeled as an unconstrained optimization problem.Then,a track association method based on particle swarm optimization(PSO)is proposed to obtain the track matrix of scattering centers with defects.Then,a method of reconstructing the missing track data based on polynomial fitting is proposed to obtain the complete track matrix of the scattering center.On this basis,the three-dimensional structure of the scattering center of the target is reconstructed by using the factorization method.The simulation results of point target verify the effectiveness of the proposed method.