Millimeter-Wave Dielectric Properties of Highly Refractive Single Crystals Characterized by Waveguide Cavity Resonance

This paper reports precision measurements of the electromagnetic permittivity of five highly refractive, single-crystal materials, SrTiO₃, KTaO₃, rutile TiO₂, LiTaO₃, and LiNbO₃, using a single, well-controlled, frequency-scalable procedure over the frequency ranges 25-110 and 140-220 GHz. Real permittivity values were highly consistent for different samples measured across multiple frequency bands. For SrTiO₃, KTaO₃, and TiO₂, real permittivities were more consistent with lower frequency values than typically reported in the millimeter-wave region of the spectrum. Real permittivities of LiTaO₃ and LiNbO₃ agreed with most reported data. The intrinsic dielectric loss of SrTiO₃, KTaO₃, and the extraordinary axis of rutile TiO₂ was also characterized over the ranges 25-110 and 140-220 GHz, and intrinsic loss per unit frequency was found to be consistent with values measured at other frequencies by dielectric resonators and quasi-optical techniques.