On Apr 12, 6:39 am, "Wes" wrote:

As far as I'm concerned, Gamma is the complex reflection coefficient;
rho is its magnitude.

As far as I'm concerned, S11 = (Z-Zo)/(Z+Zo), and is commonly known as
the (port 1) reflection coefficient, and Zo = 50+j0 unless otherwise
specified -- and |S11| is the magnitude of that reflection
coefficient. If I see rho without a definition, I only have its
context to go by, and in some circles that's pretty weak and often
inaccurate. For other ports of a multiport network, of course, S22,
S33, and so forth serve.

Almost all I need to know about a TEM line can be expressed by the set
of 2-port S parameters versus frequency for the line. Normal coaxial
and open-wire lines come about as close as anything I work with to
being true linear systems. However, the two-port model covers only
the differential TEM propagation on the line, not the line versus
ground: it's not useful for analyzing the "antenna" currents on a
line. It also doesn't tell me whether lost power is lost to heating
or to radiation, and it doesn't tell me about radiation received by
the line. The S parameter set for the line can be referenced to 50
ohms (or any other useful impedance), independent of the impedance of
the line. With the S parameter set, I can determine power loss, power
transmission, images, ... all the usual things. Of course, it's not
the only way to characterize the line, but it's complete and accurate
to the extent the line really does behave linearly and that only the
TEM propagation is important. The line doesn't even have to be
uniform; it can be exponentially expanding, or have ripples in its
impedance. If the line isn't uniform, the S parameters won't be able
to tell you power dissipation versus distance along the line, but
they'll still give you net power dissipation under specified
conditions of excitation and load.

Cheers,
Tom