| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 92 === Because of the filtering property suggested, two-dimensional periodic screens which were named the frequency selective surfaces (FSS) have attracted a great deal of attention for many years and have been found various applications, such as band-pass radomes, reflectors of antenna system, polarizers and so on. The frequency response of FSS highly depends on the configurations and spacing of the elements as well as on the thickness and permittivity of dielectric layers that may be part of the screens.
When an incident field propagates through FSS, surface currents will be induced on the conducting screens and then, in turn, radiate a scattered field. In this thesis, we employ the spectral Galerkin method to analyze the scattering phenomena of the FSS. In the spectral domain, Floquet’s theorem allows the induced surface currents to be expressed in terms of a Fourier series and reduces the computation domain from an infinite array into a single cell. For the FSS with multilayered structures, we also employ the spectral immitance approach to derive the spectral dyadic Green’s functions which relate the induced surface currents to the scattered field.
Moreover, to be more feasible for analyzing FSS with complex configurations, the subdomain basis functions are adopted to expand the induced currents. Although that will increase the number of unknowns, the computation speed can be improved by using a fast Fourier transform based iterative approach (the conjugate gradient method, FFTCG). After the distribution of the induced surface currents is determined, the spectral scattered fields can be found. Finally, we can express the reflection and transmission coefficients at different Floquet modes in terms of the spectral scattered fields at the top and bottom surfaces of the FSS.
Results for the free-standing and the single-layered-dielectric FSS with various geometries are presented, and are compared with existing results to check the correctness of our programming. In addition, some parameters, such as the configurations of the conducting screens, the thickness and the permittivity of the dielectric layers, which describe the structure of the FSS are varied to investigate the resultant effects on the frequency response.
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