Stability of the FDTD algorithm on nonorthogonal grids related to the spatial interpolation scheme

In this paper we present a reformulation of the FDTD algorithm on nonorthogonal grids, which was originally proposed by Holland in 1983. Based on the matrix-vector notation of the finite integration technique (FIT), the new formulation allows to study a special type of instability, which is due to the spatial discretization and independent of the choice of the timestep. It is shown, that this type of instability can be avoided by a symmetric evaluation of the metric coefficients of the nonorthogonal grid. Two numerical examples demonstrate the stability properties and the high accuracy of the new method.