Unconditionally Stable SFDTD Algorithm for Solving Oblique Incident Wave on Periodic Structures

In this letter, the alternating-direction-implicit (ADI) technique is applied to spectral finite-difference time-domain (SFDTD) method, resulting in an ADI-SFDTD method. It holds the advantages of both ADI-FDTD and SFDTD, not only eliminating the restriction of the Courant-Friedrich-Levy (CFL), but also solving the oblique incident wave on periodic structures conveniently. In order to save the CPU running time, the Sherman-Morrison formula is used to solve the untridiagonal linear systems. To reduce the numerical dispersion error, the optimized procedure is also applied. The accuracy and efficiency of the proposed method is verified by comparing the results with the conventional results.