Investigation of an uniform excitation scheme for accuracy and memory efficiency in microstrip FD-TD applications

Abstract

One of the important and basic requirements to ensure an accurate implementation of the three-dimensional full-wave FD-TD method is to provide an accurate source pulse for the broadband simulations of microstrip circuits. In this paper, we examine the effects of discretising the excitation plane, where the Gaussian pulse is generated along a microstrip line, with different number of rectangular grids. It is shown that the effective dielectric constants computed from the resulting electric fields under the strip are different when compared to Kirschning and Jansen's rigorous full-wave formula for four different discretisations. And, it is discovered that the launched pulse must be allowed a certain distance of travel to reach its true modal nature along the microstrip line, before it can accurately interact with the microstrip circuits. Accurate analyses of substrates with two very different permittivities substantiate the findings. The results obtained here recommend that, for accurate experimental microstrip measurements, a minimum distance between the microwave discontinuities and the coax-to-microstrip transitions should be provided.