Analysis of accuracy and stability of FDTD subgridding schemes

FDTD subgridding schemes with separated spatial and temporal subgrid interfaces were first implemented in the framework of a commercial software. The accuracy of spatial and temporal interpolation and the stability due to material traverse of these FDTD subgridding schemes were then analyzed by carrying out a number of numerical experiments. It concludes that the imperfect constant time interpolation method majorly affects the accuracy of the results at the high frequency end. However, the accuracy of the subgridding schemes mostly depends on the spatial interpolation methods rather than the time interpolation methods. It is also demonstrated that the FDTD subgridding schemes are still stable even when there are objects which traverse the spatial and temporal interfaces. However, the errors due to the material traverse are significant and it is therefore not recommended to locate any important structures across the subgrid interfaces.