  This paper presents a method for the fast and accurate estimation of the gain
pattern and maximum gain of an implanted antenna including the effect of the
host body, under the assumption that the latter is electrically large. The
estimation procedure is based on the radiation of an elementary dipole source
placed in a planar body model. The derivation of closed-form expressions is
based on spherical wave analysis and the Green's functions for layered media.
The validity of this approximation for practical cases is shown on different
implanted antennas, where the results are compared to full wave simulations and
measurements.
