An investigation into the properties of the FDTD mesh with application to wires and strips

The analysis of structures which contain thin wires or narrow microstrips using the FDTD method and without resorting to a very fine mesh, has been an area of intensive research for many years. Despite this activity, however, the problem is still not definitively solved. In this paper the problem is attacked by investigating the properties of the FDTD mesh when the material parameters of a single cell, or a small group of cells, are altered. From this, formulae are derived by which these parameters may be chosen in order to accurately represent a conductor of small cross-section. Results are presented which show that accurate results for wire and microstrip transmission lines can be achieved with little or no computational overhead and without the problems of late time instability or spurious field divergence.