Analysis And Optimization Of EM Characteristics Of Periodically Reactance-Loaded Multilayer Dielectric Structures

Periodically reactance-loaded layered dielectric structures are widely used in the design of radomes and other frequency selective structures. The frequency selective characteristic of the layered structures is a function of reactance cell form, geometric dimension and array parameters. The dielectric substrates influence frequency characteristics as well. It is significant to carry on numerical analysis of their EM performance and structural optimization. In this dissertation, both numerical method and analytical method are applied to analyze the EM scattering characteristics of periodically reactance-loaded multilayer dielectric structures. Firstly, the principle of finite element is introduced and used to analyze dielectric discontinues in waveguides. In this way, finite element mathematic model and the kernel program are verified. Then, theoretical model of finite element combined with Floquet theorem is established, and computing software is developed to analyzing the scattering of unbounded periodically structures. To increase the degrees of freedom when designing periodically reactance-loaded structure, uniaxial dielectric layer is introduced. The characteristic of multilayer dielectric plane structure with uniaxial medium and three-layer gratings are analyzed, and frequency response of scattering parameters is obtained in the case of oblique incidence. Because discrete meshes of finite element can match arbitrary geometry and dielectric structures perfectly, this method is suitable for complicated periodic structures and complicated dielectrics. In order to meet the needs of fast computation in engineering, the metal gratings are simulated with an equivalent characteristic impedance provided that the radius of the wire and the space between two adjacent wires are small enough. The equivalence model is combined with transfer matrix method, and the formula of transmission coefficient of the equivalent dielectric slab of radome wall with half wavelength thickness is obtained. Setting the transmission coefficient as fitness function in genetic algorithm, and optimizing the material, thickness, metal grating's space and radius in the radome wall, the structural parameters satisfying the prescribed requirement are obtained.