Z-parameters measurement in active circuits

Question

What difficulty faced in measuring Z parameters in active circuits, how is it taken care of?,what is limitation at high frequency?

I heard that we use inductor instead of open ckt and capacitor instead of short ckt, but how it works?

Answer 1

Some transistors like to oscillate, given some values of inductance and capacitance, without the use of dampening resistors.

Thus S-params were developed, so the transistors get measured in nominally controlled impedance systems, where the L and C gets hidden inside damped Resistive terminations.