Spectral Analysis of a Finite-Difference Frequency-Domain Solver Based on the Quasi-TEM Approximation

A finite-difference frequency-domain (FDFD) solver, based on the quasi-TEM approximation, is analyzed to determine the validity of the quasi-TEM approximation as a function of frequency. A full-wave finite-difference time-domain characteristics in a transmission line structure (stripline) at frequencies in the vicinity of the lowest waveguide mode cutoff frequency. Results show that the transverse fields in the stripline are near constant over a wide range of frequencies, even at frequencies above the dominant waveguide mode cutoff frequency.