Analysis Of Frequency Selective Surfaces Using The Finite Difference Time Domain (FDTD) Method

Frequency selective surfaces (FSS) are planar, periodic arrays of conducting patches on a substrate and / or superstate or a periodic array of apertures in a conducting sheet. These are a kind of planar periodic structure which has the character of filtering. In fact they can be regarded as a spatial filter. While the method of moments is well suited for analyzing thin, planar, patch-type of FSS elements, the same can't be said for arbitrary elements that have a finite thickness, and are inhomogeneous in nature, while FDTD algorithm is well deal with the effect of thickness on the frequency response of an FSS. The method is general enough to handle arbitrary elements as well.In this thesis, the finite difference time domain method is used to analyze the scattering characteristic of frequency selective surfaces. First, the Maxwell's equation and the basics of the FDTD technique are outlined followed by the time interval and space interval of the differential equations can be determined by analysis of stabilization and the theory of numerical dispersion. Then the boundary conditions including periodic boundary and absorbing boundary required to simulate a frequency selective surface with FDTD are discussed and the generation of a plane wave source is then described. In order to accurately model the interaction of incident light with a FSS, the electromagnetic properties of these materials must be accounted for in FDTD analysis. Material models such as Drude model is introduced to build Auxiliary Differential Equations, three dimensional simultaneous equations are established by ADEs and Maxwell's equations for simulating the FSS. According to the above-mentioned theory, three-dimensional FDTD programs are developed. These programs analysis of the frequency selective surfaces accurately and effectively. Using these programs, metals with constant or infinite conductivity referred to as ideal metal are first researched. Simulation results generated by the program are tally closely with computed and experimental results found in the literature. Then test a patch-type FSS structure which is composed of plasma and analysis the impact of basic parameters of plasma upon FSS resonant frequency. Finally a patch-type FSS structures which are made up of real metal are tested. Comparing the results of generated by the program and the computed results, all of that also showed that the FDTD can be simulate FSS correctly and effectively.