Ian White GM3SEK wrote:
Agreed. It all comes back to "usefulness" or "utility" again. As I said,
concepts are only useful if they help us to think more clearly about
physical reality - and "virtual reflection coefficient" has exactly the
opposite effect.

Also, please note that in an S-Parameter analysis, all
reflection coefficients are physical, not virtual.
Since I may have used the term first here, let me
explain what I meant by it. a1, b1, a2, and b2 are
the S-Parameter normalized voltages. Below, a1=10,
b1=0, b2=14.14, and a2=10. s11 is the physical reflection
coefficient encountered by forward wave a1. s11 is
(291.4-50)/(291.4+50) = 0.707. In an S-Parameter,
the reflection coefficient is NOT the ratio of b1/a1.

a1-- b2--
--b1 --a2
100w---50 ohm line---+---1/2WL 291.4 ohm line---50 ohm load
Vfor1=100V-- Vfor2=241.4V--
--Vref1=0V --Vref2=170.7V

Given the actual voltages, someone might say the reflection
coefficient is Vref1/Vfor1 = 0. That is a virtual reflection
coefficient. The physical reflection coefficient at point '+'
remains at 0.707. Vfor1 sees a virtual impedance of 50 ohms
at point '+' during steady-state because of the wave cancellation
that results in a net Vref1=0. But the physical reflection
coefficient doesn't change from power-up through steady-state.
One has to be careful to specify whether the physical rho,
(Z02-Z01)/(Z02+Z01), is being used or whether the virtual
rho, Vref1/Vfor1, is being used. One advantage of an S-
Parameter analysis is that virtual reflection coefficients
are not used and all reflection coefficients are physical.
--
73, Cecil http://www.w5dxp.com