Jeff Liebermann wrote:
I beg to differ somewhat. In order for the reflected power to
contribute to the incident power, the reflected power would first be
attenuated by the coax loss. It would then require a substantial
mismatch at the transmitter, which is unlikely. However, assuming
there is a mismatch at the source, some of the reflected power will be
sent back to the load (antenna), after getting attenuated by the coax
for a 2nd time. There may be some contribution, but it will very very
very very small.

Reflection of a single reflected wave is not the only mechanism
that can redistribute energy back toward the load. Superposition
of two waves at the source impedance (or at an impedance
discontinuity in a feedline) accompanied by destructive
interference can accomplish a similar feat. Non-reflective glass
is a 1/4WL matching section of thin-film that accomplishes the
same thing as a Z0-match.

To the best of my knowledge, nobody is taking wave cancellation
at the source impedance into account although it may be the
major source of the redistribution of reflected energy back
toward the antenna. It's explained on the following web pages:

http://www.mellesgriot.com/products/optics/oc_2_1.htm

"Clearly, if the wavelength of the incident light and
the thickness of the film are such that a phase difference
exists between reflections of p, then *reflected wavefronts*
*interfere destructively*, and overall reflected intensity is
a minimum. If the two reflections are of equal amplitude,
then this amplitude (and hence intensity) minimum will be
zero." (Referring to 1/4 wavelength thin films.)

"In the absence of absorption or scatter, the principle of
conservation of energy indicates all 'lost' reflected intensity
will appear as *enhanced intensity in the transmitted beam*.
The sum of the reflected and transmitted beam intensities is
always equal to the incident intensity. This important fact
has been confirmed experimentally."

http://micro.magnet.fsu.edu/primer/j...ons/index.html

"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not
actually annihilated, ... All of the photon energy present in
these waves must somehow be recovered or *redistributed* in a new
direction, according to the law of energy conservation ... Instead,
upon meeting, the photons are *redistributed* to regions that permit
*constructive interference*, so the effect should be considered as
a *redistribution* of light waves and photon energy rather than
the spontaneous construction or destruction of light."

Why does almost everyone seem to consider reflection the only way
to redistribute reflected energy back toward the antenna?
--
73, Cecil http://www.w5dxp.com