Stability Considerations for MMIC LNA

Hi,

I have read a bit about transistor design for amplifiers, the parameters that are needed for stability and how to design for stability etc.

However, it seems that for the most part, stability considerations and tests such as Rollets K-factor and the mu-parameter are meant for a lone transistor and matching networks.

Now, I am not designing an amplifier myself, rather I am using a pre-designed device for a circuit I am designing. I am talking about a MMIC Low-Noise Amplifier of which I do not actually know the topology or which transistor is used.

Can one use the same tests (rollet or mu) for such amplifiers?

How about when you want to cascade several of them, does anyone know how to go about figuring out how this affect the stability?

I know for a fact that if you cascade three of these amplifiers for instance, you will get an unstable situation. Is it possible to figure out that such a cascade will turn out to be unstable using only S-parameters ?

I'm sorry if the explanation is not very good. Hope someone could shed some light on this :)

Best Regards,

Alex.