Research On Scattering Characteristics Of PEC Targets In Terahertz Band Based On PO Method

Terahertz(THz)band lies between the infrared wave and the microwave band.Researches on the Terahertz technology are started relatively late.Compared with other wave band,THz wave has special penetrating power,which is quite safe when used for material detection and imaging.In addition,THz wave has advantages of strong capacity of resisting disturbance,large capacity and high security for communication.The electrical size of electromagnetic(EM)targets are usual y very large in terahertz band.In this situation,it will cost too much computing time and memory to deal with electrical y-large problems by employing traditional numerical methods.High frequency methods,like Physical Optics method,have such advantages as fast-computing,less time-consuming and meanwhile,the result precision are still high,though not so accurate.So in some circumstances,it is quite convenient to handle problems of electrical y-large targets by using high frequency methods.This thesis mainly focuses on the electromagnetic scattering characteristics in terahertz band.The facets grouping algorithm is taken to accelerate the occlusion judgment in PO method,then the methods for 3D rough target modeling is proposed and at the final part,the electromagnetic scattering characteristics of targets coated with plasma are calculated by using PO method related to plasma sheath.The main works are as follows:Firstly,the basic concepts and theory of PO method is introduced and then,the traditional occlusion judgment algorithm.The bi-static RCS of a sphere and a dihedral corner reflector are calculated by exploiting PO method and MLFMM method respectively,which demonstrates the application range of PO method.The most time-consuming process of PO method is occlusion judgment.In THz band,the electrical size of targets are usual y very large,which results in that this part will cost much more time.So the facet grouping algorithm is introduced to accelerate the occlusion judgment,and the efficiency is analyzed theoretically.In this algorithm,the facets of the targets are divided into many groups respectively,and by taking occlusion judgment only for close facets,numerous redundant judgment are avoided,which reduces the cost of time significantly.Since THz wave has high resolution,so the surface that looks smooth in lower frequency becomes rough,that is,the micro-structure and roughness will appear when detected by THz wave.The roughness may has a significant impact on the EM scattering characteristics of targets.Based on the 2D rough target modeling theory,the 3D rough target modeling method is developed by split-project method.This method firstly splits the surface of the target into several parts,then project them into proper coordinate planes respectively and final y generates a new 3D rough target by the mapping relationships of the points on the 2D rough surface and the projection area.The EM scattering characteristics of blunt nosed cone(BNC)and hypersonic test vehicle(HTV-2)have been presented and the effects of surface roughness on the EM scattering characteristics of targets show very well by this method.THz technology is a promising way to solve the “blackout” problem in the reentry process of aircrafts.By combining the PO method and layered medium theory,under certain conditions,the EM scattering characteristics of BNC and HTV-2 are calculated at the wave band from low frequency to THz.Finally,some meaningful results are obtained.