Narrow strip above ground plane transmission line formulation in the FDTD algorithm

A number of thin wire formalisms for use in the FDTD method have been published over the years. One such formalism was published by Holland and Simpson (IEEE Trans., EMC-23, no. 2, pp. 88-97, 1981). Later, Ledfelt (Ph.D. Dissertation, Royal Institute of Technology, Stockholm, 2001) enhanced the method in order to improve the accuracy for arbitrarily positioned wires by using a "shell average" in order to derive the average electric field around the wire. This approach was further developed by Edelvik (Tech. Report no. 2002-016, Uppsala University, Sweden, 2002), who introduced a newly defined basis function to represent the current density around the wire. Very recently Koh et al (IEE Proc. 2004) extended this approach to allow wire transmission line problems to be treated. In this paper the methods used in Koh et al are, for the first time, applied to the treatment of narrow strips with various terminations. It is shown that, with the correct choice of in-cell inductance and the appropriate use of tri-linear distribution and shell-average interpolation, accurate results can be obtained without the need for a fine FDTD mesh.