Study On The Electromagnetic Scattering From The Rough Surface Over A Frequency Band Based On The Method Of Moments

The method of moments(MoM)is widely used to simulate the electromagnetic(EM)scattering from the rough surface due to its high accuracy.However,only one frequency of the incident wave can be simulated at one time.When simulating the EM scattering over a frequency band,the MoM program is needed to be repeatedly run at each discrete frequency point.In this thesis,based on the MoM,the Maehly approximation(Maehly)is applied to obtain the rational function of the EM scattering from rough surface over a frequency band.But the traditional plane triangular surface is used to discrete the EM model of the rough surface in the Maehly approximation.Using this discrete way,it will generate a large number of unknowns,a large memory requirement and a long computing time.In this thesis,the non_uniform rational B-spline(NURBS)surface is applied to discrete the EM model of the rough surface.And in the NURBS,the number of unknowns is obviously reduced.Then the NURBS technique is combined with the Maehly approximation to get the rational function of the EM scattering from rough surface over a frequency band.Main works of this thesis are as following:1.The traditional plane triangular surface is used to simulate the EM scattering from a three-dimensional(3-D)rough surface.Firstly,the Monte-Carlo technique is used to establish the model of the 3-D rough surface.Then the traditional plane triangular surface is applied to discrete the model of the 3-D rough surface.And the RWG vector basis function is selected as the basis function.Finally,the derivation process of matrix equations is elaborated in detail.2.Two kinds of wave are applied as the incident wave for the rough surface.The characteristics of the EM scattering from the 3-D rough surface with different incident waves are discussed.The fundamentals of the inverse synthetic aperture radar(ISAR)is given.The FEKO software is used to calculate the radar cross section from the rough surface.And,the two-dimensional ISAR image of the rough surface is shown.From the ISAR image,it is shown that the result is not satisfactory if the plane wave is used as the incident wave.3.Only one frequency of the incident wave can be simulated at one time in the MoM.To simulate the EM scattering from the rough surface over a frequency band,the MoM program is needed to be repeatedly run at each discrete frequency point.Here,the Maehly is introduced to get the rational function of the EM scattering from rough surface over a frequency band.And the effectiveness of the Mahely approximation is shown by comparing the numerical results is with the repeated results of the MoM.4.To overcome the large number of unknowns of the traditional plane triangular surface in the Maehly approximation,the NURBS surface is applied to discrete the EM model of the rough surface.The principles of the NURBS surface,the roof-top basis function and the razor-blade weight function are given.The electric field integral equation is applied to simulate the EM scattering from the rough surface.Finally,the NURBS surface is combined with the maehly approximation to simulate the EM scattering from rough surface over a frequency band.