Antenna Simulations Using TLM Method and Evanescent Modes Filtration in the Lumped Elements

This article revisits the concept of localized elements in Transmission-Line Matrix (TLM) method, especially, the localized voltage source that is usually used to feed the antennas. Note that with this kind of lumped elements one can measure the current that goes through and voltage across it, hence, one can compute its input impedance and reflection coefficients. It has been shown empirically that such lumped elements are immune to evanescent modes, i.e., the measured current and voltage across its terminals are not perturbed by the evanescent EM-fields in the vicinity of the antenna, around discontinuities. The goal of this article is to explain this phenomenon and to present some simulations that confirm it.