amplifier stability considerations

hi what are the stability considerations for any amplifier (RF POWERAMPLIFIERS).
How to measure the stability of any amplifier.
how can we predict that amplifier is stable or not.
can we measure it by using spectrum analyser.
please need a clarification...


thanks in advance
@ram

Stability is "esentially and ideally" measured by using Load Pull Tuner.But this is a pretty expensive and time consuming process.
Another method is to use VNA and then obtaining s-parameters, stability factor is calculated but this method is NOT guaranteed because inner stage can oscillate an you may not see this effect in s-parameters.It often works but should be carefully..
The most practical and quite accurate method is to use a Spectrum Analyzer to observe any oscillation up to fmax ( Maximum Oscillation Frequency of the used active devices , generally it might be very high).This method is straightforward and accurate but limited to input and output terminations that are generally 50 Ohm.But the amplifier can oscillate with diffeent loading and sourcing conditions, nobody can guarantee that..

thanks Mr.big boss.
While measuring stability by using spectrum analyser,simply we have to terminate input port of the amplifier with termination or connect the input port to signal generator and observe the output in spectrum for oscillations without RF Signal and by biasing it with proper bias conditions.
Is it the correct way to measure oscillations.
please clarify me
Regards
RAM

Yep, this is the method which I mentioned above..
Again, this method is useful but limited to terminations and SA's max Frequency that is generally lower than fmax.