Near-Field Scattering Characteristics Of Electrically Large Targets In Sea Environment Based On Time Domain Shooting And Bouncing Ray

With the rapid development of radar observation of sea targets in military and civil fields,the research on electromagnetic scattering characteristics of target and sea surface composite environment has attracted more and more attention.The scattering of sea targets is not only affected by the scattering of the sea surface,but also disturbed by the coupling effect between the target and the sea surface;In addition,in the detection of electrically large targets or the terminal guidance stage of missile borne radar guidance head,the distance between radar and target is difficult to meet the far-field conditions of radiation,and the scattering characteristics in the near-field condition are more complex than those in the farfield condition.Therefore,it is necessary to study the time-domain near-field scattering characteristics in the composite environment of target and sea surface.Based on the timedomain shooting and bouncing Ray ray method,the scattering characteristics and echoes of sea targets illuminated by arbitrary pattern antennas are simulated and analyzed,and the echoes of radar moving targets are calculated and studied by using the time-domain shooting and bouncing ray method and "stop go" method.The main research contents of this thesis are as follows:1.According to the conditions of scattering near-field and far-field division and the excitation of arbitrary pattern antenna,this thesis gives the area fraction formula of timedomain physical optics when the conductor target is in the near-field radiation region of the antenna under the irradiation of arbitrary pattern antenna,and rewrites the area fraction of time-domain physical optics into a closed expression suitable for triangular integral domain by Radon transform,The fast calculation of scattering near field by time-domain physical optics method is realized.2.The use of time-domain shooting and bouncing ray method makes up for the disadvantage that the time-domain physical optics method can not calculate multiple bouncing.The generation of ray tube uses the target surface discretization method instead of the virtual aperture surface method to reduce the number of initial ray tubes,and uses the KD tree structure to store the surface elements to improve the efficiency of ray tube tracking.The intersection judgment between a single ray and the surface elements is accelerated by pulker transform,Then the tracing formula of ray field intensity in the case of conductor target is deduced,and finally the fast calculation of scattered near field by time-domain shooting and bouncing ray method under arbitrary pattern excitation is realized.3.The improved fractal sea surface model is used to generate the sea surface profile,and the formulas of time-domain physical optics method and time-domain shooting and bouncing ray method in the case of medium are deduced.Then the sea surface and target are integrated and modeled for unified ray tracing.The total scattering fields of the target and the sea surface can be obtained by calculating and superimposing the corresponding ray field intensity tracking and time-domain physical optics integration formula for the panel elements of different materials.4.A radar moving target echo model based on time domain shooting and bouncing ray method and "stop go" method is proposed.The "stop go" method is used to convert the dynamic model into a quasi-static model,and the time-domain shooting and bouncing ray method is used to calculate the time-domain echo.Finally,the motion parameter information of the target is extracted by processing the echo.