Jim Kelley wrote:

Cecil Moore wrote:
What I was trying to point out is the similarities between
Dr. Best's QEX article term, 2*sqrt(P1)*sqrt(P2)*cos(theta),
In _Optics_, Hecht's interference term 2*sqrt(I1*I2)*cos(theta),
and the above 2*s11*s12*a1*a2(cos theta) term. Seems to me, they
are all interference terms. If (0 deg = theta 90 deg) then the
interference is constructive. If (90 deg theta = 180 deg) then
the interference is destructive.

(a + b) * (a + b) = a^2 + 2ab + b^2

Wow, I made my own "interference term"!

Yep, assuming those are phasor voltages normalized to the
square root of Z0, you sure did. That's one of the advantages
of an s-parameter analysis. With the voltages normalized to
the square root of Z0, the square of any voltage equals
V^2/Z0 = power.

a^2 would be P1, b^2 would be P2, and 2ab would equal to
2*sqrt(P1)*sqrt(P2)*cos(theta) [phase angle between a and b]
--
73, Cecil, W5DXP