FDTD Subcell Modeling of the Inner Conductor of the Coaxial Feed: Accuracy and Convergence Analysis

In this paper, we analyze the method of exciting and truncating the coaxial probe used to excite an electromagnetically coupled patch antenna. The goal of the analysis is to avoid the unstable and unreliable behavior of finite-difference time-domain (FDTD) solution. The model considered here is based on the subcell thin wire modeling of inner conductor of a coaxial probe. Two main categories of structures and excitation models are considered. In the first category, the truncated thin wire is separated from the absorbing boundary by two FDTD cells, for several excitation models and their location along the wire. In the second category, the thin wire is extended into the absorbing boundary, and both the hard and the resistive source models are investigated. The comparison of the results for the two aforementioned categories of the FDTD coaxial probe feeds may be of particular interest to computational electromagnetics community, as it may yield insight into the limitations of the most commercial software packages which do not allow for extension of the coaxial probe model into the absorbing boundary.