High-temperature millimeter-wave dielectric measurements by free-space techniques

Experimental measurement techniques have been developed for utilizing spot-focusing and collimating lens antennas to determine the millimeter-wave dielectric properties of planar samples over the frequency range 30–140 GHz at temperatures up to 1600°C. The method is suitable for studying the average bulk-sample dielectric properties as well as inhomogeneities on the dimensional scale of a wavelength. Other significant advantages of the method include: thermal isolation of the sample from the measurement apparatus, minimum sample preparation requirements, and convenience for screening a large number of samples in relatively short time periods. The measurement apparatus has been used to study a wide variety of materials, which has led to successful models for explaining the observed temperature dependence of the dielectric properties of polycrystalline ceramics.