On the FDTD Near-to-Far-Field Transformations for Weakly Scattering Objects

Recently published papers on the near-to-far-field (NTFF) transformation in the finite-difference time-domain (FDTD) method have demonstrated accuracy improvements for weakly scattering objects. The improvements are achieved by modifications of the “standard” NTFF transformation which is based on interpolation of the spatially shifted fields in the FDTD grid. In this paper, it is shown that accurate results can be obtained for such weakly scattering objects without the suggested improvements, provided that the correct FDTD NTFF transformation is used. “Correct” is referred to a transformation procedure that is consistent with the FDTD version of the equivalence principle. This NTFF transformation procedure was published in the IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION in 1998. Recently published results for weakly scattering objects have been reproduced using this NTFF transformation.