What is meant by resonance in microstrip patch antenna ?

what is meant by resonance in an antenna ?
please explain in reference to microstrip patch antenna.

Resonance in an antenna means that the antenna's impedance behaves similar to the impedance of an LCR circuit (within a limited frequency band).

Especially half wave patch antennas with small height/lambda ratio have a high Q-factor and therefore have small relative bandwidth. Generally spoken, all antennas that have to operate parallel and close to a large metal surface behave like narrow band LCR circuit. Depending on feed scheme, they can have parallel or series resonant behavior.

A half wave patch behaves as a parallel resonant circuit when probe fed or fed at an edge.

When I simulate a patch antenna, how can I see that it is resonant?
The impedance and thus the S11 depends on the feed location, so I can't use this parameter.