How can an open loop RF active circuit have a positive S11?

[skatefast08]

How can an open loop RF active circuit have a positive S11? As the Keysight ADS oscillator design guide says you need to make sure the S11 is on the RHP or encircling the 1+j0 point. What causes this to happen? If I want to create my own oscillator from a transistor, how would you pick the correct one, so that you will get S11 encircling the 1+j0? Thanks

 

[BigBoss]

This is necessary and sufficient condition for oscillation and it depends on not only transistor but on many factors. You have to follow the Design Steps of an Oscillator. Start to read Randall Rhaea' s textbook.