Here are some papers, programs, and links that let you become more familiar with finite difference time domain (FDTD) solvers for Maxwell’s Equations.
A paper by D.W. Ward, and K.A. Nelson (”Finite-difference time-domain (FDTD) simulations of electromagnetic wave propagation using a spreadsheet,” Comput. Appl. Eng. Educ., 13: 213-221 (2005)) teaches you the idea of FDTD by building a simple [...]
