Poles and zeroes in two port parameters (passive structures)

[Joel Kolstad]

Would anyone have a pointer to where I might found information about the
'allowable' S-plane locations for poles and zeroes in two port networks
parameters for passive structures, specifically Y, Z, and S parameters?

These are my thoughts:

-- Whatever applies to Y probably applies as Z as well.
-- Since Z11, Z22, Y11, and Y22 can all be seen as simple input
impedances/admittances, none of them should have right half-plane (RHP)
poles OR ZEROES.
-- Z12, Z21, Y12, and Y21 probably can't have RHP poles but probably can
have RHP zeroes.
-- S parameters are a complex enough transformation that it's unclear to me
whether or not there are any particular restrictions.

The reason I ask... I generate equivalent circuit models from measurement
data using curve fitting; the results are in the form of a rational
polynomial that can be readily factored to its pole/zero formulation. It'd
be nice to have an 'eyeball' method of ensuring the resultant ECM is stable.

Pointers to network theory books discussing this would also be appreciated.

Thanks,
---Joel Kolstad