Accurate Measurements of Material Properties at Microwave Frequencies

The microwave part of the electromagnetic spectrum is particularly relevant for any application involving security, defense, and aerospace. As such, accurate characterizations of materials in this frequency range are of utmost relevance to enable proper design of devices, or prediction of the response of materials (coatings, conductors, dielectrics) to microwave irradiation. In this paper we present a novel resonant measuring system able to measure both the surface resistance $R_{s}$ of conductors and the complex permittivity $\epsilon'-i\epsilon''$ of dielectrics. The experimental system is based on a custom-designed sapphire-loaded cylindrical resonator working at ~13 GHz. We show that the setup overcomes the repeatability issues that often affect resonant systems, and it is easy to operate. Measurements reach uncertainties ~1mΩ in differential measurements for the surface resistance, and relative uncertainties of 5% and 10% in $\epsilon'$ and $\epsilon $ respectively.