Without calibration, measurements refer to instrument front panel connectors as refernce plane. Purpose of calibration is to eliminate the effect of cables and connectors. Single port measurements, e.g. antenna impedance should be referenced to DUT interface.
If the antenna has a local connector, we would preferably perform a reflection calibration (SOL, short, open load) at the antenna. Because antennas have usually a wide S parameter range so that small deviations don't matter, it can be sufficient to add a "port extension" to calibration parameters, in other words shift the reference plane by a known cable length without considering cable or connector non-ideality.