Full wave analysis of HTS superconducting microstrip transmission lines using spectral-domain immittance approach

This paper presents a modified spectral domain immittance approach method used for full-wave analysis of high-temperature superconducting microstrip transmission lines. A strip transformation technique is used to transform the thin superconducting film into infinitely thin strip of infinite conductivity. In this technique the superconducting strip is treated as an impedance sheet which introduces new boundary conditions at the surface of the strip. Enforcing these new boundary conditions in the Fourier domain introduces some modification to the diagonal elements of the Green's impedance matrix, in the spectral domain, of the microstrip structure. An efficient computer program was developed to search for the complex roots of eigenvalue equation using Muller's method. The effective dielectric constant for several HTS microstrip transmission lines were computed using our program. The comparison between these results and published data indicated the validity of our program in estimating the dispersion characteristics of superconducting microstrip lines having high film-to-substrate thickness ratio.