Line-of-sight approximation to the equivalence principle

A line-of-sight (LoS) approximation to the equivalence principle used in far-field computations is proposed. In the LoS equivalence, only the surface currents at the virtual surface and the edge currents at its contour, which are on the LoS with the observation point, are used in the calculation of the radiated field. It is a far more efficient alternative to the standard equivalence principle, which requires integration over the entire closed virtual surface. We present the theory associated with the LoS equivalence approach, examine the error due to the approximation, and demonstrate its accuracy via the radiation of dipole antennas.