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Cecil Moore · August 26th 06, 01:37 PM posted to rec.radio.amateur.antenna

wrote:
Cecil Moore wrote:

If I understand correctly, Roy's argument is that since
the source is not supplying any steady-state energy to
the lossless stub, there is no energy in the reflected
wave within the stub.

That sounds right... if the reflection coefficient is 1 then there's no
net power flux into/through the line in steady state, and this can be
described if you like by counterpropagating waves each carrying the
same amount of energy.

If the counterpropagating waves each carry the same amount
of energy then there cannot be zero energy in the reflected
wave.

Some people on this newsgroup say that the wave reflection
model is invalid, that forward and reflected waves don't
have a separate existence. From QEX: "Contrary to popular
views, the forward and reverse waves on a transmission line
are not separate fields." It would follow that a laser beam
normally incident upon an ideal mirror results in a beam of
light not superposed from separate forward and reverse fields.

I have challenged people holding those concepts to create a
standing wave without superposing separate forward and
reverse waves and have gotten zero responses.

The problem is, in your other example where you say 200 joules in the
forward wave + 100 joules in the reflected wave = 300 joules in the
line total, you're neglecting the vector character of the power flux.

I apologize if I accidentally gave that wrong impression.
I subscribe to Ramo/Whinnery's notion that the power reflection
coefficient is equal to the reflected Poynting vector divided by
the forward Poynting vector. Pz-/Pz+ = |rho|^2

Yes, the waves carry energy, but they carry it in different directions.
The net power flux in the line with 200W forward power and 100W
reflected power is 100W net power flowing to the load from the source.
The real part of the Poynting vector of the reflected wave opposes that
of the forward wave, as long as I got all the signs right.

Yes, that's what I am saying. The other side would assert that
there is no reflected Poynting vector and no forward Poynting
vector - that there only exists the net Poynting vector. This
is a change away from mainstream RF engineering taught in the
1950's. The "modern" concept seems to be that forward and
reflected waves don't exist. All that exists are the standing
wave and the net forward traveling wave with nothing moving
backwards.
--
73, Cecil http://www.qsl.net/w5dxp