Permittivity of highly absorbing oxide ceramics in millimeter waves

Complex dielectric permittivity of highly absorbing oxide ceramics have been studied in a broadband millimeter wave frequency range for the first time. Transmittance and reflectance measurements have been performed using a free space quasi-optical spectrometer, equipped with a set of high power backward wave oscillators, tunable in Q-, V- and W-frequency bands. Ceramic materials have found to be almost non-transparent (opaque) in millimeter waves with extremely high values of permittivity. Frequency dependences of dielectric permittivity, calculated from precision transmittance and reflectance spectra are presented.