I. INTRODUCTION
Recently, the complementary operators method (COM) was presented as a new FDTD boundary truncation scheme [1]. This method uses two complementary boundary operators whose reflection coefficients are identically opposite. The first order reflections from the truncated boundary are canceled by performing two independent simulations. In the concurrent version of this method, termed C-COM [2], the two complementary operators are employed concurrently in the same simulation, thus the computation is reduced about one half. In C-COM, the errors caused by the first order reflection for traveling waves and evanescent waves can be annihilated completely in any directions, and the errors will only be in the order of the second order reflections. If a high quality absorbing boundary condition (ABC) is used as the fundamental operator, the errors will be very small. Using Higdon's ABC as the fundamental operator, C-COM has been utilized to simulate the radiation of line sources and scattering from perfectly conducting cylinders [1] [2]. It has been shown that the performance of this scheme is comparable with, or even superior to, that of the PML technique [3] for some applications.