When we study time-domain electromagnetic fields, we frequently use the finite-difference time-domain (FD-TD) method. In this paper, we discuss errors of the FD-TD method and present the optimum mesh spacings in the FD-TD method when the three mesh spacings are different.

When we use the finite-difference time-domain (FD-TD) method to study time-domain electromagnetic fields in the unbounded surroundings, we frequently use a radiation boundary condition (RBC) by means of one-way wave equations. The reflection coefficient by the RBC is independent of frequency, but the reflection coefficient of the finite difference approximation for the RBC depends on a frequency also; this study examines how the reflection characteristics are affected by the frequency, and the study presents the coefficients used in the RBC which gives expected reflection characteristics for a frequency, and presents the application to simulation of the matched termination of a rectangular waveguide.