Cecil Moore wrote:
On Jan 9, 11:22 pm, Roy Lewallen wrote:
Just what is a "wave", anyway? Are there different "kinds" of
electromagnetic wave?

Take a look at the E-field, H-field, and direction of travel for an EM
(photonic) wave. An RF standing wave does not behave like an EM wave
nor does it meet the definition of an EM wave which can be represented
by a Poynting vector. The Poynting vector for an RF standing wave has
a magnitude of zero and no direction.
--
73, Cecil, w5dxp.com

Cecil,

That is flat out wrong. For a plane wave the E and H fields are
perpendicular for either traveling waves or standing waves. For a
coaxial cable operating in the normal TEM mode, the E field is radial
and the H field is circular around the center conductor. Again, the E
field and H field are always perpendicular. Unless one or both of the
fields are exactly zero, the Poynting vector will be nonzero. It will
have a magnitude and direction.

I suppose what you are looking at is some sort of time average. In that
case the average of the Poynting vector at a single point in space may
be different for standing waves and traveling waves. However, that
information is essentially useless. The only thing with physical
reality, related to Poynting vectors, is the integral of the Poynting
vector over a closed surface. Equivalently, the only thing with physical
reality is the divergence of the Poynting vector.

In the lossless cases we are typically discussing, the time-averaged
integral or the divergence is exactly zero for either the traveling wave
case or the standing wave case. The Poynting vector is no help in making
any sort of distinction at all.

73,
Gene
W4SZ