This paper reports a quantitative characterization of a poly-SiGe MEMS-based Xylophone Bar Magnetometer (XBM), thereby following a novel characterization method that is based on the measurement of the forward/backward transmission gains S 21 /S 21 of the XBM treated as a two-port network. More specifically, this was done through monitoring the absolute amplitude of the resonant peaks of S 21 and S 12 with changing magnetic induction B. Also, we present for the first time a novel equivalent circuit for the two-port XBM, modeling effectively the electro-magneto-mechanical behavior of the magnetometer. The experimental measurements showed that poly-SiGe XBM is capable of being a linear magnetic sensor in mT range with a sensitivity 0.1dB=mT with an excitation power 5dBm fed to the electrodynamic/electrostatic port and a biasing voltage 14V applied through the sense/drive capacitor.