Mode Excitation and Radiation Characteristics of Antennas in Cylindrically Stratified Media

Guided modes excited by a current source in a multilayer cylindrical structure is thoroughly investigated. The guidance condition in the multilayer structure is formulated. Based on this, three antenna configurations in cylindrical stratified media that are of strong practical interest are rigorously investigated: viz. a monopole antenna, a conformal axially-directed slot antenna and an azimuthal slot antenna in a cylindrical layered medium. While previous treatments of such configurations did not investigate the mode-excitation problem of antennas in stratified cylindrical media and were limited in their applicability for a dipole antenna in a cylindrical medium or assumed the slot-current distribution for a slot antenna over a conducting cylinder only, the current investigation provides an in-depth and rigorous insight to the modes excited and power coupled to the excited modes for the antenna configurations and removes such restrictions. In addition to the efficient and rigorous investigation of the coupling problem for the three antenna structures, the radiation characteristics of the antenna configurations are also evaluated using the method of stationary phase, enabling a comprehensive treatment of the antenna structures from both the coupling and radiation aspects.