Roy Lewallen wrote:
So where do you draw the required surface over which to integrate the
Poynting vector and thus obtain the "reflected power"?

As you know, a one-dimensional transmission line is a lot easier to
work with than the 3D space involved with radiation from antennas.
In fact, all we need for a transmission line Poynting vector is
a plane. Since the field area of the coax is constant and known, we
can treat it as a constant normalized value. It allows us to come
up with a simplified version of what you posted. Quoting from,
"Fields and Waves in Communications Electronics", by Ramo, Whinnery,
and Van Duzer: "... we are often most interested in the ratio of power
in the reflected wave to that in the incident wave, and this ratio is
given by ...

Pz-/Pz+ = |rho|^2"

where Pz- is the reflected power Poynting vector, Pz+ is the forward
power Poynting vector, and rho is the reflection coefficient. Pretty
simple stuff that I learned 45 years ago. Again from the same book:

Pz+ = (E+)x(H+) and Pz- = -(E-)x(H-)
--
73, Cecil http://www.qsl.net/w5dxp



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