Abstract
When using sub-cell algorithms to model the coupling of apertures with finite depth in the finite-difference time-domain (FDTD) method, time-step size is required to be reduced to avoid instability. In this work, a time-step program is proposed for the stable modeling of apertures with finite depth using sub-cell algorithms. A sub-cell area related time-step reduction coefficient is introduced to ease the steady reduction of the time-step size firstly. Then a modified algorithm is given for sub-cells whose area is extremely distorted. Numerical results demonstrate that the proposed time-step program is an accurate and stable modeling of aperture coupling without resulting in significant time-step reduction.