A low-cost instrument for the accurate measurement of Whispering-Gallery resonances up to 19 GHz

The main current limit to the application of Sapphire Whispering Gallery Thermometry (SWGT) as transfer temperature standard in industry is represented by the cost and bulkiness of the Vector Network Analyzer (VNA) required to investigate the resonances of interest. In this work we present a low-cost measurement system for the accurate detection of complex resonance frequencies up to 19 GHz, aimed at replacing the use of a VNA in those field applications where portability and cost-saving are crucial requirements. The system includes a low cost GPS-based solution to obtain the needed accurate and stable frequency reference. The proposed equipment has been tested on a SWGT and successfully validated comparing the results obtained with a state-of-the-art laboratory set-up comprising a wideband VNA and a rubidium frequency standard. Results obtained demonstrated the potential of the system to replace VNAs in SWGT applications.