High temperature permittivity measurements of Alumina Enhanced Thermal Barrier (AETB-8) material for CEV antenna radomes

Alumina Enhanced Thermal Barrier (AEBT-8) material is currently being considered as a potential radome material for phased array antennas that will be conformally mounted to the outer surface of NASA´s Orion Crew Exploration Vehicle. Accordingly, there is a need to establish if the dielectric properties of the AEBT-8 material change as a function of temperature. In this paper we discuss the measurements of the real (ε_r´) and imaginary (ε_r´´) parts of the dielectric constant of AEBT-8 at temperatures from 25- 900°C and in the frequency range from 2-18 GHz. Our results show that neither ε_r´ or ε_r´´ showed a measurable temperature dependence when tested in the aforementioned temperature range. Comparison at room temperature to measurements taken using the waveguide technique showed good agreement for ε_r´, but the ε_r´´ values for the AETB-8 material are so low that diffraction phenomena limits the accuracy of the results obtained using the free space technique.