Anomalous dispersion region is a resonance signature in the frequency response of resonators known as Lorentz resonators. It is identified by two consecutive slope reversals of the transmission phase response and a dip in the amplitude response. In this letter, we propose to exploit this unique resonant phase signature in characterization of the conductivity of solid and liquid material samples. The microwave resonator sensor consists of an open microstrip stub whose conductivity is designed to vary in response to an intruding sample. The transmission response of the resonator containing the material sample is measured using a vector network analyzer. The change of conductivity affects the Q-factor which can be detected by either the slope changes of the anomalous dispersive phase or the 3dB bandwidth of the amplitude spectrum. The hypothesis is practically demonstrated by detecting resistive changes of a saline solution whose conductivity depends on the amounts of additive salt.
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