Abstract: An implicit finite difference time domain method using the principle of alternating direction implicit technique is unconditionally stable, and the maximum time step size is not limited by the CFL condition, but rather by numerical errors.Compared with the conventional FDTD method, the time step size of ADI-FDTD can be much larger, so it takes less time to simulate.In this paper ADI-FDTD is applied to simulate the scattering of three-dimensional targets in vacuum and the settings of excitation and total-field/scattered-field connecting boundary condition are derived.Compared with FDTD, the results of ADI-FDTD have the same lev el of accuracy as conventional FDTD and the CPU cost is obviously reduced.

Key words: FDTD, scattering, ADI