Open resonator for precision dielectric measurements in the 100 GHz band

Dielectric properties of fused silica, MgO, AlN, and BN were measured using an open resonator at frequencies around 100 GHz. The resonator is of the semifocal type and consists of a concave and a plane mirror, and the frequency variation method is used. To increase the reliability of measurement data, the operating frequency and thickness of the samples were chosen so as to make the parameter Δ=1 for every sample. The radius of curvature of the concave mirror is deduced with sufficient accuracy from the resonant frequencies of the transverse-electric-mode TEM_0.0 and TEM_1.0 modes, which results in a precise determination of resonator length. The standard deviation of measurements was less than 0.1% in permittivity and about 10% in loss tangent