Microwave characterisation of CaF2 at cryogenic temperatures using a dielectric resonator technique

Properties of calcium fluoride (CaF2) have been well researched at UV, visible and IR range of frequencies but not at microwave frequencies. In this work we report the loss tangent and the real part of relative permittivity εr of CaF2 measured in the temperature range 15–81 K and at frequency 29.25 GHz. The tanδ and εr were determined by measurements of the resonant frequency and the Q0-factor of a TE011 mode cylindrical copper cavity with superconducting plates containing the sample under test. The measured εr of CaF2 was found to change from 6.484 to 6.505, and the tanδ from 3.1×10−6 to 22.7×10−6 when temperature was varied from 15 to 81 K. Due to the low losses CaF2 can be useful in construction of high Q-factor microwave circuits and devices operating at cryogenic temperatures.