On Jun 16, 1:48*am, Owen Duffy wrote:
Prs is not simply equal to the 'reflected power'.

I don't remember anyone saying that Prs is equal to the reflected
power and of course it is not. What you guys are missing are the
effects accompanying interference from superposition. There is another
mechanism besides the reflection mechanism that can redistribute the
reflected power. The power density equation includes an interference
term that indicates what happens to the energy.

Prs = Pfor + Pref + 2*SQRT(Pfor*Pref)*cos(A)

This equation gives the same answer as your equation but it also
indicates what happens to the energy components. A is the phase angle
between Vfor and Vref. The last term is the *interference* term.

If the interference term is zero, there is no interference and all of
the reflected power is dissipated in Rs.

If the interference term is negative, there exists destructive
interference at Rs and power is redistributed toward the load as
constructive interference. This is technically not a reflection
although the results are the same as a reflection.

If the interference term is positive, there exists constructive
interference at Rs and excess power is dissipated in Rs.

Let's look at your equation, Prs=(Vs/2-Vr)^2/Rs

Vfor = Vs/2, so Prs = (Vfor+Vref)^2/Rs (phasor addition)

Prs = Vfor^2/Rs + Vref^2/Rs + 2*Vfor*Vref*cos(A)/Rs

Prs = Pfor + Pref + 2*SQRT(Pfor*Pref)*cos(A)

I just derived the power density equation (with its interference term)
from your equation. The power density equation reveals the
interference term which tells us exactly where the reflected power
goes.

I learned about destructive and constructive interference at Texas A&M
in the 1950s.
--
73, Cecil, w5dxp.com