Cable loss to antenna will reduce the forward, then return reflected power.
It can be calibrated out but the round trip loss reduces the dynamic range of network analyzer by the round trip dB loss. If you are looking to get impedance at the antenna you must calibrate out the cable because you also need the phase information correct for network analyzer to figure terminal impedance at end of cable.
Also on NanoVNA, when measuring antennas you have to be careful of strong nearby radio transmitters, like AM or FM broadcast stations. The input mixer chip of NanoVNA can be overloaded by strong RF signals.
