> An isolator is linear except with frequency just as a cap or
> inductor or feedline are.
No, it's not linear. First off, it doesn't satisfy the superposition
principle since it will produce harmonic when fed by a pure sinusoid carrier
(hopefully we can agree to that without added discussion), so right off the
bat it's nonlinear. Furthermore, it's also non-reciprocal; what enters port
1 exits port 2 with little loss, but the converse is not true.
> What's in an isolator that is
> non-linear.
Ferrite.
> It is made of transmission lines, no active
> components
There's no requirement that there needs to be an active component for the
device or system to be non-linear. A diode is a passive device and it's
certainly not linear.
--- Jeff
