Auto-tuning and self-calibration of high-sensitivity radio frequency interferometers

We demonstrate a technique that automatically tunes the sensitivity of a radio-frequency (RF) interferometer with a tunable liquid attenuator by accurately changing its liquid volume. The obtained effective quality factor (Qeff) of the interferometer is up to 1 × 108 at ∼5 GHz. The Qeff is ∼100 times higher than previously reported results. When material-under-test (MUT), i.e., methanol-water solution in this work, is used for the tuning, a self-calibration and measurement process is demonstrated from 2 to 7.5 GHz at a methanol concentration level down to 5 × 10-5 mole fraction, which is 100 times lower than previously reported results. Further investigations are needed to achieve better system stability and higher sensitivity. © 2016 IEEE.