Sub-gridding FDTD Algorithm for 3D Numerical Analysis of EM Scattering and Radiation Problems

The finite-difference time-domain (FDTD) method is used effectively to solve electromagnetic (EM) scattering and radiation problems using a 3D sub-gridding algorithm. For accuracy and stability of the FDTD method, the computational domain of EM problems with locally fine structures or electrically small objects is discretized with finer grids. This sub-gridding algorithm for different regions of the computational domain was implemented to increase the accuracy and reduce the computational time and memory requirements compared to those of the traditional FDTD method. In the sub-gridding algorithm, the FDTD computational domain is divided into separate regions: coarse grid and fine grid regions. Since the cell sizes and time steps are different in the coarse and fine grid regions, interpolations in both time and space are used to evaluate the electric and magnetic fields on the boundaries between different regions. The accuracy of the developed 3D sub-gridding algorithm has been verified for radiation and scattering problems, including multiple fine grid regions. Excellent performance is obtained even for higher and different contrast ratios in fine grid regions.