Quality Factor Estimation of Microwave Resonator-Based Sensors Using PLL-Based Resonance Tracking on an SDR Platform

The quality factor (Q-factor) is a key parameter for resonant sensors, as it quantifies energy losses and is directly related to sensor sensitivity and resolution. Although several time- and frequency-domain techniques have been proposed for Q-factor measurement, achieving fast and reliable estimation remains challenging, particularly for in-line applications. This paper presents a Q-factor estimation method implemented on a software-defined radio platform with a LabVIEW interface. The proposed approach dynamically computes the Q-factor from the averaged resonance and half-power frequencies using a phase-tracking system based on a phase-locked loop architecture. Experimental results demonstrate that the implemented algorithm estimates the Q-factor within a total measurement time between 5 s and 20 s, with relative deviations ranging from 0.1% to 3.4%.