An unconditionally stable subcell model for arbitrarily oriented thin wires in the FETD method

A computational subcell model for thin wires is developed for electromagnetic simulations. The Maxwell equations are discretized by a finite element approximation on a tetrahedral grid. The wires are described by a second-order equation for the current. The geometry of the wires can be chosen independent of the volume grid. A symmetric coupling between field and wires yields a stable semi-discrete field-wire system and an unconditionally stable fully discrete field-wire system. The system of equations is in each time step solved by a preconditioned conjugate gradient method. The accuracy of the subcell model is demonstrated for dipole and loop antennas with comparisons with the method of moments and experimental data.

I. Introduction

The ability to model features that are small relative to the cell size is often important in electromagnetic simulations. In principle, an unstructured grid could be used to resolve these small features. However, the increase in number of unknowns can be prohibitive. Thus, the development of accurate models that characterize the physics of the feature without the need for a highly resolved grid is important.