The Method Of Moments In Time Domain (MOMTD) And Its Applications To Radiation And Scattering Problem

The aim of this thesis is to apply the method of moments in time domain(MOMTD)and the hybrid method that efficiently combines MOMTD and the finite difference time domain(FDTD)simulating the electromagnetic radiating and scattering of complex objects. The main works of author are as follows: a)Based on the method of moments(MOM), considering that the total tangential electric field is zero on the metal wire surface, we can educe the electric fields integral equation of an arbitrarily shape thin wire antennas, and get the iterative formula for the surface current of antennas. Its applications to radiation and scattering problems are very good, and it possesses the preferable stability and accuracy. b)In order to improve the late-time oscillations of using march on in time(MOT) technique in calculating the electric fields integral equation, the implicit MOT and explicit MOT arithmetic is investigated. These two approaches both possess the preferable stability and accuracy. In particular, the time-domain electric integral equation of second-order time differential coefficient is calculated by an explicit MOT solution. The vector potential terms are approximated with the center of the edge. The scalar potential terms are approximated with the centroid of the triangular patch. Then five step and three step averaging techniques are adopted, which can improve the convergence and stability of the TDIE method efficiently. c)Due to the complexity of practical electromagnetic problems, the single numerical and analytical method has not been able to satisfy its demand. Therefore the hybrid methods, which combine the desirable features of two or more different techniques, have become a developmental trend. In order to have a perfect matching with FDTD, achieving an iterative explicit, the hybrid method that efficiently combines FDTD and MOMTD is investigated comprehensively. The hybrid method is applicable to complex geometries comprising arbitrary thin-wire and inhomogeneous dielectric structures. It employs the equivalence theorem to separate the original problem into two subproblems: 1) the region containing the wires, which is analyzed by using the MOMTD, and 2) the dielectric zone that is modeled with the FDTD.