In three-dimensional space, the hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method is weakly conditionally stable, only determined by two space-discretizations, which is very useful for problems with fine structures in one direction. Its numerical dispersion errors with nonuniform cells are discussed and compared in this paper. To enlarge the applicable field of the HIE-FDTD method to open space, the absorbing boundary conditions (ABCs) for this method are also introduced and applied. Two microstrip filters with fine scale structures in one direction are solved by the HIE-FDTD method. Conventional FDTD method and alternating-direction implicit FDTD (ADI-FDTD) method are also used for comparing. Results analyzed by the HIE-FDTD method agree well with those from conventional FDTD, and the required central process unit (CPU) time is much less than that of the ADI-FDTD method.
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