High Linearity Microwave Displacement Sensor

This article presents a new planar microwave sensor for displacement measurements. The sensor is based on a modified triangular-shaped quarter-wavelength resonator that has the advantage of maintaining its linearity throughout the required displacement range due to its reduced ground capacitance when compared to conventional resonators. Designs of three different sensors are shown for displacement ranges of 4, 14, and 24 mm. Their figure of merit (FoM) is FoM =0.5 for the 4-mm sensor, 0.7 for the 14-mm sensor, and 0.97 for the 24-mm sensor. Moreover, the midrange sensor (14 mm) was manufactured to operate in a frequency range from 700 MHz to 2 GHz having an FoM =0.7. This sensor is operated using a vector network analyzer (VNA) and an alternative reflectometer board for onsite applications. The experimental values show errors of less than 4% when comparing the VNA and the reflectometer results.