Low-Cost Instrument for Whispering Gallery Mode Thermometry up to 19 GHz

In this paper, a portable low-cost system for the accurate measurement of complex resonance frequencies up to 19 GHz for whispering gallery mode thermometry is presented and validated. The instrument performs vectorial transmission measurements for the determination of resonance frequencies with accuracy in the order of a few parts in 10^9 over two different RF/microwave bands: 1) 800 MHz–7 GHz and 2) 13–19 GHz. The former band is suitable for quasi-spherical resonator (QSR)-based experiments, currently of great interest in different metrological applications, while the latter is expressly supported for whispering gallery thermometry. The capability of the instrument to meet the performance required for whispering gallery thermometry is first verified using an extremely stable setup based on a QSR. Afterward, the calibration of the whispering gallery thermometer composed of the developed instrument and an existing resonator is performed. The obtained results prove the suitability of the instrument to replace vector network analyzers in accurate resonance-based experiments and also its capability to enable the use of whispering gallery thermometers as transfer standards in the industrial field.