Dielectric characterisation of Barium Fluorideat cryogenic temperatures using TE011 and quasi TE0mn mode dielectric resonators

Abstract

Barium Fluoride (BaF2), mainly used in optical applications, has similar properties to those of CaF2 but better stability under environmental conditions. In this paper, we report measurements of loss tangent and the real part of the relative permittivity εr of single crystal BaF2 in the temperature range from 14 to 290 K at frequencies of 8, 10.4, 12.1, 17.6, 21.1 and 24.4 GHz. Microwave properties of BaF2 were determined by measurements of the resonance frequency and the unloaded Q-factor of TE011 and quasi TE0mn modes cylindrical cavities containing the sample under test. Two techniques namely Hakki–Coleman Dielectric Resonator and dielectric post resonators have been used for characterizing the dielectric material. Losses due to the uncalibrated cables and adaptors inside the cryocooler are accounted in the calculation of unloaded Q-factor using the Transmission Mode Q-Factor data processing technique. The permittivity of BaF2 exhibited a 5% increase from 6.9 (14 K) to 7.35 (290 K). The loss tangent increased from 1 × 10−5 to 1.1 × 10−4 over the measured temperature range, 14–290 K at a frequency of 10.4 GHz. The measured microwave properties show that BaF2 can be used in many microwave devices.