Resonant frequency of resonator

[Lathas]

How to determine the exact resonant freq of a transmission line resonator from simulation? Is it the peak of S21 or the angle of Y21 =0?

 

[PA4TIM]

The transition where the S21 phase jumps from 180 degrees to -180 degrees , so the phase jump, and resonance is where -jX is equal to +jX so phase must be zero degrees.
This is called phase resonance. Normaly the S21 magnitude trace will peak max or min on at that point depending on the resonator (parallel or series)
I do not know how Y parameters behave in a S parameter measurement.

Z are impedance parameters, Y are admittance parametersd, S are scattering parameters, you have more lijke h, T, abcd parameters.