Cecil,

Radio amateurs and "magic antenna" charlatans love to abuse Poynting
vectors and the Poynting theorem.

The basic answer is no, it is not correct to say, "the power in an EM
wave was [is] defined as ExH."

The Poynting vector, generally described as ExH, is the energy flow
density. It has units of energy/area/time. While this may seem to be
nitpicking it is essential to note that this vector is defined at a
point, not for a "wave", and an integration (or summation) over the
surface of a closed volume must be performed before one can say anything
about power or conservation of energy.

In practical terms the Poynting vector ExH and the Poynting theorem have
little utility for radio amateurs.

73,
Gene
W4SZ

Cecil Moore wrote:

Roy Lewallen wrote:

I strongly suggest forgetting completely about "forward" and "reverse"
power. If you must deal with directional waves, look at forward and
reverse voltage and current waves.


Say Roy, exactly how many of those EM voltage and current waves
have you encountered that didn't possess any energy? I always
thought the power in an EM wave was defined as ExH. :-)
--
73, Cecil http://www.qsl.net/w5dxp