A monitoring/calibrating system is provided based on the amplitude and/or phase of electric and/or magnetic fields measurements. In transmitter mode of AUT, one or more probe sets are placed very close to the AUT around the radiation aperture of AUT to prevent probes effects on the AUT performance. For each amplitude/phase state of AUT controller, the near field data are measured and compared with a previously stored dataset. A successive method can reduce the error by changing the amplitude/phase of AUT controller. Moreover, a machine learning method can be used to classify the errors in near field data, errors in amplitude/phase of AUT controller, and automatically tuning the AUT controller. In receiver mode of AUT, the system is the same but the probe sets are working as transmitters to make a known near field around the AUT.