NUMERICAL STABILITY OF FINITE-DIFFERENCE TIME-DOMAIN METHODS

Recently, several modifications of Yee's well known FDTD method to loc ally refined grids or non-orthogonal coordinates have been presented. These methods sometimes show an unexpected unstable behavior. In this paper we will classify such instabilities in order to derive rules how to avoid them. As an example, we present a long term numerically stab le subgridding scheme which will be examined by regarding a microstrip phase shifter.