Theoretical Research On Electromagnetic Wave Propagation In Transverse Cascaded Wave-Guides And Multi-layered Structures

Theoretical analysis on electromagnetic wave propagation in inhomogeneous media plays an important role in the fields of wireless communication and microstrip circuits applications,etc.In the recent decades,there have been more researches of antenna and wave propagation in high frequency circuits than theoretical research on wave propagation in low frequencies which is necessary to be continued;on the other hand,along with the discovery of new materials,sur-face wave propagation has attracted more and more attentions on multi-layered structures.Based on theory of wave propagation in inhomogeneous media,the thesis investigates on the charac-teristics of VLF wave propagation in cascaded terrestrial waveguide with abrupt equivalent ion-osphere height,and the method to solve the trapped surface wave in the presence of planar mul-tilayer structure.The main work is summarized as follows:1.The characteristics of VLF wave propagation in terrestrial waveguides are studied.Since the TM modes and TE modes are coupled due to the influence of the Earth magnetic's field to ionosphere environment,the attenuation rates and phase velocities of VLF wave are given when subjected to different Earth magnetic's field intensity.Besides,the interference behavior of VLF propagation modes has been studied with the spatial distribution.2.The expression of mode-conversion coefficients is derived for VLF wave at the junction between two cascaded waveguides representing for day and night status,respectively.Specifi-cally,the field components described by Airy functions,boundary conditions,two-port analysis are considered for the derivation of mode-conversion coefficient with abrupt heights of equiva-lent ionosphere;in addition,the formulas are extended into more general case with varying height condition.Finally,numerical calculation is carried out for discussion of mode contribu-tions.3.Based on the mode-conversion coefficients,the total fields in the reflected and scattered regions are evaluated,respectively,for the VLF electromagnetic wave propagating across the diurnal transition region.On the propagating path,the phenomenon of mode-conversion inter-ference for VLF wave is analyzed.The amplitude and phase of VLF electromagnetic wave are evaluated.The feasibility of calculations is verified by comparing with the measured data.4.The analytical solution of electromagnetic wave in the presence of stratified media is studied due to a vertical electric dipole.At first,the relationship between pole roots is investi-gated.The traditional algorithm for root finding is improved by meshing,the relationship be-tween pole roots and dielectric length is enhanced;then,the Sommerfeld integrals are studied for evaluations.The direct wave,ideal reflected wave,lateral wave and trapped surface wave are discussed,respectively,on and above the air-to-dielectric boundary.Finally,the propagation characteristics of each component of electromagnetic wave and its contribution to the total field are illustrated by an example.5.The analytical solution for root finding of pole equation in the presence of N-layer re-gion is presented.By using mathematical deduction,an improved pole equation based on gener-alized coefficients is established,which transformed the original pole equation with nested ex-pression into a simplified expression.By simplifying the pole expression,it greatly simplifies the difficulty of solving poles by numerical and analytical methods.This could provide some theoretical references and help for the application in multi-layered structures design.