Reflection-Type Open-Ended Parallel-Plate Type Sensor for Direct Broadband Dielectric Spectroscopy of Liquid Chemicals with Simplified Calibration

A novel one-port microwave sensor is proposed, which is dedicated for direct broadband dielectric spectroscopy of liquid chemical. An open-ended parallel-plate transmission line is realized out of sheet metal to extend past the host printed circuit board, thus the sensed complex permittivity is directly the permittivity of measured liquid-under-test. The sensor is fed by a double-sided parallel stripline which interconnects through a broadband transition to a microstrip input line, which are later de-embedded using a single open standard. A simplified calibration technique that requires only one measurement in air is employed to establish all calibration constants. The sensor was utilized for measurements of various alcohols in a high cm-wave range proving the usability of the proposed circuit for liquid material characterization.