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

In reason of their extremely high accuracy in the determination of microwave resonance frequencies, quasi-spherical cavities are key instruments for pursuing a variety of metrological applications, spanning from the realization of primary temperature and pressure standards, to the determination of the electrical properties of pure gases and mixtures, including hygrometry. Also, the simple and rugged design and features of quasi-spherical resonators make them suitable for industrial applications in harsh environments over extended temperature and pressure ranges. In traditional laboratory practice, Vector Network Analyzers are needed to fully exploit the precision achievable in the measurement of the cavity eigenfrequencies. However, the cost and bulkiness of this instrumentation currently limit the applicability of these techniques and methods. This work presents and discusses the design of a low cost microwave instrument which may finally replace vector network analyzers while maintaining the precision and accuracy required for most applications.