Numerical techniques to compute the cutoff frequencies, modal fields, and dispersion characteristics in microwave planar media

Numerical techniques for calculating modal fields, cutoff frequencies, and dispersion characteristics in shielded microwave planar transmission media are developed. The formulation uses the method of images to derive a Fourier series expression for the current on the inner conductor, a one-dimensional Green's function (which was derived by transforming Maxwell's equations into the spectral domain) to evaluate the electric field, and point matching in the moment method to find the source-free solution. To decrease computation time and to improve the representation of the slowly-converging electric fields, an acceleration technique is used.The formulation described in the previous paragraph has been applied to two geometries, the homogeneously-filled boxed stripline (BSL) and the shielded microstrip transmission line (SMTL). Results are given which include the current distribution on the inner conductor, cutoff frequencies for the different types of modes, three-dimensional plots of the modal field components, and stream-line plots of the transverse modal fields. One of the methods used to validate the computer code is to view the presence of the inner conductor as a perturbation to an empty waveguide and a slab-loaded waveguide (SLWG), and to compare the cutoff frequencies and streamline plots for the different structures. Dispersion characteristics for the SMTL are also computed and compared to those reported by other authors.Besides comparing the modal fields to known fields in the empty waveguide and the SLWG, the computer code is validated by (1) computing the tangential electric field along the inner conductor and evaluating how well the boundary conditions are met, (2) comparing results with other authors, and (3) comparing computed cutoff frequencies for TM modes in the SMTL with the measured resonant frequencies of a cavity with the same cross section.U of I OnlyETDs are only available to UIUC Users without author permissio