Hybrid Methods Based On EB-FEM And Their Applications To The EM Problems Of Electrically Large Complex Cavities

The analysis of electrically large complex cavity is an important topic in the field of computational electromagnetics. It is meaningful to the development of stealth and anti-stealth technology, electromagnetic compatibility of electronic equipments as well as the design of some relevant microwave devices.Edge-based finite element method (EB-FEM) is an efficient numerical method for the analyses of electromagnetic characteristics of complex objects. The conception of EB-FEM was firstly proposed by Whitney in 1957. Not until the beginning of 1980's, the importance of EB-FEM in electromagnetic computation has been realized. From then on, EB-FEM has been developed quickly. In 1990's, J. M. Jin and J. L. Volakis combined EB-FEM with other numerical methods and successfully applied them to the analyses of a variety of electromagnetic problems.Aiming at efficient analyses of electromagnetic characteristics of electrically large complex cavities, some hybrid techniques are developed based on EB-FEM, including IPO/FEM, extended IPO, improved IPO/FEM, DDM/FEM-BIE, DDM/FEM-PO-PTD, FEM/IBC, and FEM/PML. The following contributions have been made in this dissertation:A novel hybrid approach is proposed in which iterative physical optics (IPO) subdomain-splicing technique is combined with EB-FEM, the mathematical model of the proposed IPO/FEM is established by some approximate methods. It is applied to theanalyses of electromagnetic scattering by electrically large complex cavities. The compressed coefficient matrix is stored and other memory saving methods are involved. SSOR is employed to improve the coefficient matrix, as a result, FEM solver-BICG is speeded.Iterative physical optics is extended to the analysis of electromagnetic scattering by dielectric coated targets. The theoretical model of the extended IPO is formulated by Fresnel reflection coefficient. It is applied to analyze the scattering by geometrically simple, electrically large, dielectric coated cavities. And then the extended IPO hybridized with FEM is employed for the analysis of electromagnetic scattering by dielectric coated, electrically large cavities with complex terminal. Green's functions of the dielectric coated board is involved. As a result, the IPO would be more accurate by employing the Green's functions to compute the interactions of facets on the same plane.The hybrid approach of EB-FEM combined with domain decomposition method (DDM) and boundary integral equation (BIE) is introduced. Overlapping, nonoverlapping and overrelaxation DDM are discussed. Electromagnetic (EM) scattering by electrically large open-ended cavities is analyzed by DDM/FEM-BIE. And then a hybrid technique combining DDM with EB-FEM, PO, and PTD is given for the analysis of electromagnetic scattering by electrically large bodies with deep cavities.Dielectric discontinuities in waveguides are analyzed by EB-FEM in combination with perfectly matched layer (PML) absorbing boundary condition (ABC) .The influences of the number of dielectric blocks and the permittivity of the dielectric blocks on the S parameters are discussed. Some useful conclusions are drawn, EB-FEM is combined with Leontovich IBC here to analyze the electromagnetic scattering by a cavity coated with layered medium. The multi-reflection of the electromagnetic wave in the medium is involved, and the precision of the method is improved.