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

Free-space measurement techniques can be contactless and are able to accommodate large, flat sheets of dielectric material, making them useful for characterization of high-temperature, 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 \boldsymbol {\epsilon }_{r}^\prime 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 \boldsymbol {\epsilon }_{r}^{\prime \prime } value of 0.032 ± 0.007. At 25 °C, the \boldsymbol {\epsilon }_{r}^{\prime \prime } 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