  In this tutorial, we discuss the radiation from a Hertzian dipole into
uniform isotropic lossy media of infinite extent. If the medium is lossless,
the radiated power propagates to infinity, and the apparent dissipation is
measured by the radiation resistance of the dipole. If the medium is lossy, the
power exponentially decays, and the physical meaning of radiation resistance
needs clarification. Here, we present explicit calculations of the power
absorbed in the infinite lossy host space and discuss the limit of zero losses.
We show that the input impedance of dipole antennas contains a
radiation-resistance contribution which does not depend on the imaginary part
of the refractive index. This fact means that the power delivered by dipole
antennas to surrounding space always contains a contribution from far fields
unless the real part of the refractive index is zero. Based on this
understanding, we discuss the fundamental limitations of power coupling between
two antennas and possibilities of removing the limit imposed by radiation
damping.
