Passivity of S-parameters is an important topic since so many of the S-parameter files you get from component manufacturers were poorly measured and are in fact not passive.  Of course here we're just talking about passive components such as resistors, capacitors and inductors.

If you use non-passive S-parameters when modeling your circuit you will often see strange results (depending on just how much gain the components have) and this is especially true if you run noise simulations.

Anytime you use S-parameters the first thing you should do is run a passivity check on them which is easy to do in MWO.  In this project we show how to use the PASSIVE measurement and show how a typical component model (right off a vendor's website) is non-passive.

If you have any questions, comments or suggestions on this article please post as a comment.