In this paper an approach to efficient computation of radiation pattern in FDTD simulation environment is presented. A necessary large distance from the radiating object is achieved by multigrid space discretization with unilaterally connected subdomains. A numerical dispersion is reduced using more general complex-envelope finite difference time domain (CE-FDTD) formulation and high order accuracy FDTD schemes where possible. In order to examine how much the introduced algorithm complexity and increased demands concerning computational power and memory are justified by the gain in accuracy, several different scenarios were considered.