New FDTD method to estimate the dielectric constant and loss tangent of a bilayer dielectric material at x-band frequencies

Abstract

In this paper, a new iterative method is presented to estimate the dielectric constant and loss tangent for each layer in a Bi-layer dielectric material using an X-band short-circuited rectangular waveguide WR90. The S11-parameter at the reference plane as a function of dielectric constant and loss tangent of each layer is calculated by applying the two-dimensional finite difference in time-domain method (2DFDTD) for the wave equation. Then, the Nelder-Mead algorithm is applied to estimate the dielectric constant and the loss tangent by matching the measured and calculated S11-parameter. This method has been validated on three bi-layer dielectric materials such as Teflon-FR4 Epoxy and FR4 Epoxy-Plexiglas and Plexiglas-Teflon. A comparison of estimated values of the dielectric constant and loss tangent obtained from FDTD-2D Maxwell's equations measurements and 2D-FDTD Wave equation measurements is presented. Remarkably, this method reduces the execution time by a factor of five while maintaining equal precision.