An analysis of the coax-fed monopole in a general medium

A coax-fed monopole antenna in a general linear medium is investigated theoretically and results are corroborated experimentally. The monopole resides in a general lossy medium above a ground plane and is formed by the extension of the center conductor of a coaxial waveguide whose outer conductor terminates in the ground plane. The excitation is the usual TEM field in a coax. The analysis is sufficiently general to accommodate a bead of prescribed dielectric properties to support and center the coax inner conductor. Coupled integral equations are derived for the monopole current and for the electric field in the annular aperture formed where the coaxial guide joins the ground plane. These equations account for the higher order modes in the coaxial guide. A numerical/analytical method for solving these coupled equations is developed and implemented. Numerical results--monopole current, aperture electric field, and driving point admittance-are obtained and are compared with available experimental data. The agreement is generally excellent.