In previous chapters, the finite-difference time-domain (FDTD) method is used to compute electric and magnetic fields within a finite space around an electromagnetic object (i.e., the near-zone electromagnetic fields). In many applications, such as antennas and radar crosssection, it is necessary to find the radiation or scattered fields in the region that is far away from an antenna or scatterer. With the FDTD technique, the direct evaluation of the far field calls for an excessively large computational domain, which is not practical in applications. Instead, the far-zone electromagnetic fields are computed from the near-field FDTD data through a near-field to far-field (NF-FF) transformation technique.