The Analysis Of EM Scattering From 3-D Targets By Moment Methods

The electromagnetic field theory and numerical calculation are the research basis of electromagnetic scattering problem,they have important applications in many aspects such as calculation of Radar Cross Section(RCS),analysis of electromagnetic scattering characteristic of target,electronic countermeasures,stealth design and identification of target.The Moment Method is used to calculate the RCS of three-dimensional targets in this paper.These targets include conducting targets,dielectric targets and coat targets.Triangular patches are used to model the surface of the target,then Electric Field Integral Equation(EFIE) and Magnetic Field Integral Equation(MFIE) are built which satisfy the boundary conditions.The RWG vector base functions are used to denote equivalent electric current and magnetic current on the surface of the target.Finally use the Galerkin method (RWG vector base functions are basis function and test function) to transform integral equations into matrix equation.When obtain the equivalent electric current and magnetic current, we can calculate the scattering field and the RCS of the target.First,the conducting targets'electromagnetic scattering is researched in this paper.The RWG vector base functions are used to denote inductive current on the surface of the conducting target.EFIE is built.The RCS of conducting sphere.conducting plate,conducting cube are calculated respectively,the electromagnetic scattering of multi-rivets on the conducting plate are researched the first time,and the impaction of multi-rivets to the total RCS is analyzed.Then,the dielectric targets'electromagnetic scattering is researched.An important principle of electromagnetic field theory--equivalent theory is introduced.As well as the conducting target,the geometrical model of the dielectric target should first be built,then triangular patches are used to model the surface of the dielectric target.Different from the conducting target,there has not only equivalent electric current but also has equivalent magnetic current onthe surface of the dielectric target.So now should built two equations-EFIE and MFIE to obtain the unknown current coefficients.The RCS of dielectric sphere,dielectric cylinder,dielectric cube are calculated respectively.Finally,the coat targets'electromagnetic scattering is researched. Two cases are analyzedxonducting target with coat and dielectric target with coat.For the conducting target with coat, triangular patches are used to model the surfaces of the coat and the conducting object.Now there have equivalent electric current and magnetic current on the surface of the coat,but only has equivalent electric current on the surface of the conducting object.The RWG vector base functions are used to denote equivalent electric currents and magnetic current.Three integral equations should be built to obtain the unknown current coefficients;for the dielectric object with coat,triangular patches are used to model the surfaces of the coat and the dielectric object.Now there have equivalent electric current and magnetic current not only on the surface of the coat but also on the surface of the dielectric object.This time four integral equations should be built to obtain the unknown current coefficients.The Moment Method can not be used to analyze electrical-large size targets. Such limit is not due to the method itself,but is due to the limits of the speed and memory of computers.At present,we mainly use the high-frequency approximate method to analyze the electrical-large size target whose shape is relatively regular. But using the high-frequency approximate method to deal with the coupling of parts of electrical-large size target is troublesome as well as not accurate.Combining the Moment Method and the high-frequency approximate method is a development trend and study way in the future.