An Overmoded-Waveguide-Based Permittivity Measurement Method with High Accuracy and Ultra-Broadband over 8-110 GHz.

An overmoded-waveguide-based kit operating in 8-110 GHz for material complex permittivity measurement is proposed and designed in this paper. It overcomes the significant errors caused by air gaps in the conventional standard waveguide method (SWM), especially for millimeter-wave frequency bands. Furthermore, it avoids the problem of SWM requiring different samples in broadband measurements. The proposed kit consists of an overmoded-waveguide sample fixture with cross dimensions of 22.86 mm × 10.16 mm, seven pairs of standard-overmoded waveguide transition structures for different frequency bands, and thru-reflect-line calibration kits. The air gap problem, a major error source in millimeter-wave measurement, is quantitatively investigated. Compared with the SWM method, the proposed kit can decrease errors from over 68% to below 8%. The proposed method was verified by measuring the polytetrafluoroethylene sample. Then, it was applied to measure the BeO-TiO₂ ceramic, which is widely used in vacuum devices. The measured data are valuable for applying BeO-TiO₂ ceramics in relevant devices and developing its dielectric relaxation model.