The treatment of geometrically small structures in FDTD by the modification of assigned material parameters

A number of different improvements to the analysis by finite-difference time-domain (FDTD) of small structures, such as wires, strips and slots have been proposed in the literature. One of these methods takes account of the fringing fields associated with metal edges and wires by empirically modifying the assigned material parameters in neighboring cells. In this contribution it is shown that, in many cases, it is possible to derive these modified assigned material parameters (MAMPs) analytically. In this form, the approach provides an alternative, and novel, way of incorporating Static Field Solutions into the FDTD method which has advantages of simplicity and robustness over existing techniques. Results are presented for a number of structures including wire transmission lines and a microstrip patch antenna.