Thanks for making that clear, Tom. I should also have emphasized that
it's valid only in the far field, where the wave is essentially a plane
wave with E/H equal to the impedance of the medium.

Roy Lewallen, W7EL

Tom Bruhns wrote:
Implicit in Roy's answer, but perhaps worth stating, is that the
result is for an antenna in freespace. If you are working with an
antenna over earth, things will be different because the energy is
radiated into a hemisphere instead of isotropically, and because of
interference and diffraction patterns, and absorption by the earth,
vegetation, etc. At some frequencies, absorption by things in the
atmosphere attenuates the signal, too.

Cheers,
Tom