Techniques are described for detecting whether a phased array antenna is to be calibrated. In an example, a controller communicatively coupled with the phased array antenna measures a characteristic of a probe signal. The probe signal is communicated between an antenna element of the phased array antenna and a probe antenna mounted to the phased array antenna. The probe antenna is over-resonant. The controller further determines a drift of the phased array antenna based at least in part on the characteristic. Based at least in part on the drift, the controller initiates a calibration of the phased array antenna.