A low-cost instrument for the accurate measurement of resonances in microwave cavities

Since vector network analysis became available, it demonstrated its accuracy and versatility in a variety of applications, including the accurate measurement of resonances in microwave cavities. Unfortunately, the high cost and bulkiness of vector network analyzers (VNAs) set a limit to their applicability. This paper presents and discusses the design and the initial performance tests of a simplified instrument which may represent a valid alternative to VNAs in those applications where the high quality factors of a microwave resonator have to be determined with comparable accuracy but at low cost, allowing field portability and the embedment in a more complex measurement system. Triggered by the recent development of quasi-spherical microwave resonators and their successful utilization in gas metrology, we choose the extremely precise measurement of their eigenfrequencies as a suitable test bench to validate the specifications and assess the performance of the proposed instrument.