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

A stainless steel open-ended coaxial probe was developed to measure the com plex permittivity of solid dielectric materials at elevated temperatures an d over a broad frequency range. The spring loading of the inner conductor i nsured hat the probe maintained contact with the sample up to 1000 degrees C and eliminated errors due to differential thermal expansion of the probe. Comparison with an industry standard probe demonstrated that the spring-lo aded probe accurately and reproducibly measured the complex permittivity of several samples over a broad frequency range of 0.3-6 GHz at room temperat ure. At temperatures up to 1000 degrees C, dielectric measurements of a gla ss ceramic and of a porous alumina composite performed with both a spring-l oaded 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 insens itivity in measuring low-loss materials constrained accurate dielectric mea surements to materials with tan delta greater than or equal to 0.05, Finall y, optimization of an open-ended probe by varying the probe dimensions is p resented.