Research On High Frequency Analysis Methods For Complex Target Scattering

With the development of electromagnetic technology,high frequency electromagnetic simulation has been more and more widely used in various fields.The analysis of electromagnetic scattering characteristics of objects has become one of the important research directions of computational electromagnetics.With the increase of the frequency,the electrical size of the object also increases.When using the traditional full wave algorithms to calculate,they will occupy a lot of memory and calculation time.The emergence of high frequency asymptotic methods makes it possible to quickly predict the scattering characteristics of targets.Therefore,how to use high-frequency approximation methods to quickly predict the electromagnetic scattering characteristics of complex targets has become one of the hot issues in the current research.In this thesis,the physical optics method is used to analyze the scattering characteristics of electromagnetic targets.Based on the physical optics method,RWG basis function is used.The surface current is characterized by RWG basis function,and the radiation field is calculated by the characterization coefficient.Compared with the traditional physical optics method,RWG basis function can well characterize surface currents,and it can also calculate near-field and far-field.For the most time-consuming part of multiple occlusion judgment in physical optics,the octree structure is used to optimize it,reduce the time complexity and accelerate the judgment process.For complex composite electromagnetic targets,the equivalent reflection coefficient and transmission coefficient of multi-layer dielectric coating are calculated by using the transmission line theory.By calculating the equivalent impedance,the multilayer dielectric is coated on the metal surface,and the reflection coefficient is used to update the reflection field of the current characterization coefficient,and then the scattering field of the coated target is calculated.According to the scattering characteristics of pure dielectric objects,the surface electromagnetic current is characterized by extending the surface current to the surface electromagnetic current due to the existence of equivalent surface magnetic current on the dielectric surface.This method can not only analyze the scattering characteristics of dielectric targets,but also expand the calculation range of physical optics method.For complex environment,a image method is used to calculate half space environment problems.Mirror the original object according to the ground,judge the multiple occlusion of the original object and the mirror object,calculate the multiple effects of the ground on the incident field and scattering field,and calculate the scattering field value in the half space environment through vector superposition.Aiming at the problem that the physical optics method does not consider the influence of multiple reflections on the calculation results,this thesis applies ray path tracking and field strength tracking to the physical optics method to simulate the propagation of electromagnetic waves on the surface of scatterers.The surface electromagnetic current is characterized by calculating the field intensity after multiple reflections.Ray tracing technology is used in physical optics method,which can effectively improve the calculation accuracy and application range of physical optics method.Several examples are given and compared with commercial software to verify the correctness of the algorithm.