Study On Characteristic Mode Theory For Composite Electromagnetic Structures And Its Applications

The theory of characteristic mode(CM)only depends on the characteristics of the electromagnetic objects like the geometry,dimension,and material.At the same time,it is independent of any exterior excitations.Therefore,the process of its modal decomposition can offer the clear physical explanations on the radiaton or scattring mechanisms of the electromagnetic objects.The CM theory was initially proposed for the scattering problems of the perfectly electrically conducting(PEC)bodies.Later,it has been extensively applied to the analysis and optimization of the antenna systems with the blooming of the wireless communication.However,since the CM theory for PEC bodies is accepted and applied,the theoretical development of the CM for more complex electromagnetic structures is barely satisfactory and it severely limits its application extension.Therefore,the systematic study on the CM theory for extending its theoretical versatility is great help of the theoretical refinement of the CM.More importantly,it can physically provides the systematic guidelines on the radiation or scattering analysis for the more general electromagnetic objects.For the purpose,a number of studies on the theoretical development for the CM are carried out following the similar procedure as that in PEC CM theory in this dissertation.These studies include the development and validation of the CM theories for the fully dielectric coated conducting bodies and the arbitrarily metallic-dielectric composite bodies,the application of the CM theory for the N-port networks to the tightly coupled array.The main contents of this dissertation are as follows:1.The research backgrounds,history,and development of the CM theory are briefly reviewed.Then,starting from the electric-field-integral-equation-based(EFIE-based)method of moment(MoM),the CM theory for the PEC bodies is developed from the mathematical operator and the energy relationship,respectively.The physical meanings of the resultant eigenvalues,the orthogonality of the resultant characteristic currents and fields are also proofed through the complex Poynting's theorem.Finally,the numerical implementation process of the CM theory in computer code is demonstrated.The two of the most important computational modules,that is,solving of the generalized eigenvalue equation and CM tracking,are also detailed.2.The CM theory for the fully dielectric coated conducting bodies is developed for the first time based on the EFIE-PMCHWT surface integral equation.Through enforcing different field tangential component continuity condition over the dielectric coating surfaces,two types of generalized eigenvalue equations(GEEs)are proposed.They produce the same modal analysis results and offer powerful theoretical support for the radiation mechanism researches of the fully dielectric coated conducting bodies.Moreover,the physical meanings of the eigenvalues sovled from the GEEs are rigorously proofed following the source-free complex Poynting's theorem.The orthogonality of the resultant characteristic currents and fields are also demonstrated.Finally,based on this CM theory,two types of modal decomposition methods are proposed correspondingly for scattering analysis of the fully dielectric coated conducting bodies.This method reveals clearly the underlying scattering mechanism for the fully dielectric coated conducting bodies based on a computationally efficient scattering decomposition process.Moreover,it provides valuable information to guide systematic scattering control for the fully dielectric coated conducting bodies.3.For the first time,the contact region modeling(CRM)technique is integrated into the EFIE-PMCHWT surface integral equation for developing the CM theory for the arbitrarily metallic-dielectric composite bodies.Through enforcing different field tangential component continuity condition over the dielectric body surfaces,two types of generalized eigenvalue equations(GEEs)producing the same modal analysis results are proposed.They offer powerful modal analysis tool for the arbitrarily metallic-dielectric composite structures including the fully dielectric coated conducting bodies,partially dielectric coated conducting bodies,and partial metallic sheet coated on the dielectric bodies.Moreover,the physical meanings of the eigenvalues sovled from the GEEs are rigorously proofed following the energy balance relationship.The orthogonality of the resultant characteristic currents and fields are also demonstrated.Finally,based on this CM theory,two types of modal decomposition methods are correspondingly proposed for scattering analysis of the arbitrarily metallic-dielectric composite bodies.This method realize a computationally efficient scattering decomposition process.At the same time,it offers deep physical explanations on the scattering mechanisms of the arbitrarily metallic-dielectric composite bodies.4.The research for realizing wideband impedance matching performance of the tightly coupled dipole arrays(TCDAs)by resorting to the CM theory for the N-port networks is carried out.By equalizing the TCDA to be a multi-port network,a mutual impedance matrix representing its port characteristics can be easily extracted and the corresponding generalized eigenvalue equation(GEE)can be established.The various characteristic exciations including the port charactersitic currents and characteristic impedance are then obtained through solving the GEE.In order to realize wideband impedance matching performance,a set of wideband characteristic excitation is selected and applied to excite the TCDA.As a result,the bandwidth of each antenna element in the array is broadened and the realized gain of the whole TCDA is increased compared with the conventional uniform excitation.