Low-Cost Microwave Vector System for Liquid Properties Monitoring

In this paper, we propose a novel low-cost microwave vector system dedicated for monitoring the properties of liquid samples. The system is composed of the differentially fed coupled-line sensor and five-port correlator allowing for measurement of both magnitude and phase of a signal dependent on material under test. An exemplary microwave vector system has been designed to operate at the frequency $f_{{0}} = \text{2.4}\, \text{GHz}$, manufactured and experimentally verified. The measurement results have proven the increased sensitivity of the proposed sensor on the dielectric materials in comparison to the methods described in the literature. Moreover, the proposed sensor has been utilized for measurements of several milk samples with various fat content, and the obtained results prove the industrial application of the presented approach.