If you have be stalled when confronted with a device model specified by S-Parameters, you should read the following collection of AppNotes...
"CreateS-ParameterSubcircuitsForSpice.pdf"
now posted under the "Tools" section of the "Simulation Tools & Macros" page of my website...
Also just posted there, but only of interest to those who design microchips...
"LayoutRoutingInstructions.pdf"
some graphical techniques for passing critical metal routing information to layout personnel. (WIP: Matching to be added.) ...Jim Thompson