Substrate-Integrated Liquid-Permittivity Microwave Sensor with Simultaneous Fixed-Reference Resonance
The design of a substrate-integrated circuit for the complex dielectric permittivity estimation of liquids at microwave frequencies using a simultaneous fixed reference resonance is presented in this paper. The system is composed by a resonant cavity as the main sensor and a microstrip resonator for the fixed reference resonance. Both cavity and resonator are coupled to a single input-port by transmission lines with particular lengths for isolation between them, and end in separate output-ports. The proposed sensor design is experimentally tested using two different circuits and six liquids, and the results are corroborated with values obtained from a standard coaxial-probe measurements.