$W$ -Band Complex Permittivity Measurements at High Temperature Using Free-Space Methods

Abstract

Free-space measurement techniques can be contactless and are able to accommodate large, flat sheets of dielectric material, making them useful for characterization of hightemperature, millimeter-wave, window and radome candidate materials. As part of the present work, a high-temperature, W-band (75-110 GHz), free-space measurement system was developed and used to characterize complex dielectric properties of bulk material samples at temperatures ranging from 25 °C to 600 °C. Two test cases, polyvinyl chloride (PVC) and CoorsTek 92% alumina, were measured at 25 °C and found to have ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ' values of 2.731 ± 0.005 and 8.061 ± 0.027 at 95 GHz, respectively. The 25 °C PVC sample was measured to have a ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> " value of 0.032 ± 0.007. At 25 °C, the ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> " value of the 92% alumina sample was below the uncertainty threshold achievable with the present free-space measurement apparatus and could only be bounded to c0.009. As the alumina sample was heated to 600 °C, ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ' and ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> " values increased to 8.501 ± 0.028 and 0.035 ± 0.008, respectively. The high-temperature behavior of the authors' 92% alumina ceramic was found to be similar to that previously documented for Sumitomo AKP-50 alumina over the 25 °C-600 °C temperature range. In addition to the 92% alumina sample, three commercially available ceramic substrates (zirconium oxide, boron nitride, and silicon nitride) were also characterized at temperatures ranging from 25 °C to 600 °C.