Full-Wave Analysis of an Imperfectly-Conducting Stripline

Abstract

In this paper, the discrete principal-mode propagation constant of an imperfectly-conducting stripline field applicator is investigated. Specifically, a complex correction to the ideal (i.e., perfectly-conducting) propagation constant is sought using a full-wave spectral-domain analysis. First, the electric-field dyadic Green's function for a general three-dimensional (3D) current source immersed within an imperfectly-conducting stripline background environment is determined with the aid of Hertzian-potential impedance boundary conditions. These boundary conditions, which are developed in the paper, follow from a Leontovich boundary condition and include important coupling terms that are absent in the perfectly-conducting case. Next, the stripline structure is realized by specializing the general 3D current to a 2D current flowing in an imperfectly-conducting center strip. Boundary conditions are subsequently enforced on the center strip, leading to an electric field integral equation (EFIE). The complex propagation constant for the imperfectly-conducting stripline is found through solution of the EFIE via formulation of a non-Galerkin's method-of-moments (MoM) technique. In particular, Chebyshev expansion and testing functions of the first and second kind are implemented to closely model the strip current, to accelerate convergence and to allow resulting spatial integrals to be performed in closed form. The advantage of this full-wave analysis over the standard perturbation method is discussed and various numerical results are given for the attenuation and phase constant of the principal-mode.