Open-ended coaxial probe for high-temperature and broad-band dielectric measurements

A stainless steel open-ended coaxial probe was developed to measure the complex permittivity of solid dielectric materials at elevated temperatures and over a broad frequency range. The spring loading of the inner conductor insured that the probe maintained contact with the sample up to 1000 °C and eliminated errors due to differential thermal expansion of the probe. Comparison with an industry standard probe demonstrated that the spring-loaded probe accurately and reproducibly measured the complex permittivity of several samples over a broad frequency range of 0.3-6 GHz at room temperature. At temperatures up to 1000 °C, dielectric measurements of a glass ceramic and of a porous alumina composite performed with both a spring-loaded probe and a resonant cavity agreed to within 8% for the real part and 15% for the imaginary part of the complex permittivity. The probe's insensitivity in measuring lowloss materials constrained accurate dielectric measurements to materials with tan 5>0.05. Finally, optimization of an openended probe by varying the probe dimensions is presented.