ELIMINATION OF THE SPURIOUS ROOT IN THE SDA SOLUTION TO THE SHIELDED MICROSTRIP PROBLEM

We report that the spurious root that appears in the spectral-domain a pproach solution to the shielded lossless and infinitely thin microstr ip is eliminated when enough basis functions to accurately describe th e transverse current density are used. A fast algorithm based on the o bserved simple behavior of the minimum singular value of the character istic matrix as a function of beta(2) instead of beta is presented. Fo r lossless microstrip lines, with small values of the dielectric const ant and at relatively low frequencies, two evaluations of the characte ristic matrix are sufficient to determine its dispersion properties, w hen the longitudinal current density is assumed Maxwellian, thus achie ving a considerable reduction of CPU time. (C) 1995 John Wiley & Sons, Inc.