Improved Discrete-Time Boundary Condition for the Thin-Wire FDTD Analysis of Lossy Insulated Cylindrical Antennas Located in Lossy Media

For the thin-wire (TW) finite-difference time-domain (FDTD) analysis of lossy insulated antennas surrounded by lossy media, an improved discrete-time boundary condition (DTBC) at the interface is proposed here. In previous TW-FDTD techniques, the DTBC formulations on the material discontinuity between the lossy insulation and lossy surrounding media were derived from the dielectric constitutive relation under the uniform field approximation (UFA) over each time step. In this paper, to achieve higher accuracy, an improved DTBC is formulated from Maxwell’s equations under the linear field approximation (LFA) and subsequently corrected in the TW-FDTD update equation. By comparing the input impedances of Teflon-insulated cylindrical monopole antennas located in wet soils, we show that the proposed approach provides higher accuracy than previous techniques.