A high-temperature capable planar-type coaxial probe for complex permittivity measurements up to 40 GHz

A planar-type probe applicable to a wide temperature and frequency range has been developed. The probe employs a low CTE (Coefficient of Thermal Expansion) dielectric material to minimize the effect of thermal expansion for high temperature measurement. Additionally, the coaxial aperture dimensions have been optimized through sensitivity analysis to minimize the uncertainty of the extracted complex permittivity due to variations of the measured S-parameters. Also, the error correction method was used at extreme temperatures to compensate for the effects of the excessive thermal expansion. For validation, distilled water was measured from 0 °C to 100 °C in the frequency range of 0.5-40GHz. The measured complex permittivity shows good agreement with the reference data up to 75 °C without the error correction and up to the boiling point (92 °C) with the error correction. To our knowledge, this is the first demonstration of low-cost planar-type probes capable of high temperature operation.