In accordance with an embodiment, a measurement system includes a sensor circuit configured to provide a voltage sense signal proportional to an electric field sensed by the RF sensor and a current sense signal proportional to a magnetic field sensed by the RF sensor; an analysis circuit comprising a frequency selective demodulator circuit configured to: demodulate the voltage sense signal into a first set of analog demodulated signals according to a set of demodulation frequencies, demodulate the current sense signal into a second set of analog demodulated signals according to the set of demodulation frequencies, and determine a phase shift between the voltage sense signal and the current sense signal for at least one frequency of the set of demodulation frequencies; and analog-to-digital converters configured to receive the first and second sets of analog demodulated signals.