Broadband complex permittivity and conductivity measurements in the millimeter-wave bands over variable temperatures using a balanced-type circular disk resonator

A broadband measurement system is developed to address the issue of temperature dependence of the complex permittivity and conductivity of low-loss substrates in the millimeter-wave bands for fifth/sixth generation wireless communication applications. The developed system can provide broadband material measurements from less than 20 GHz to over 100 GHz over variable temperatures by utilizing higher order mode resonances of a balanced-type circular disk resonator (BCDR). The broadband measurement capability of the developed system is attributed to the mode-selective behavior of the BCDR over a wideband. To demonstrate the developed system, we measure the complex permittivity of the following three substrate materials over variable temperatures from 25 °C to 100 °C: cyclo-olefin polymer (COP), ceramic-filled polytetrafluoroethylene composites, and fused silica. Furthermore, the temperature dependence of the conductivity of the surface-mounted metal is characterized for the COP substrate. The measurements indicate that the loss tangents and conductivities of the substrates increase and decrease, respectively, with the temperature and frequency in the millimeter-wave bands. The full-wave simulations using the measured complex permittivity and conductivity of the COP substrate reveal that the propagation loss of the microstrip line using the COP substrate increases with the temperature and frequency and that the increase in the loss is primarily attributed to the decrease in the conductivity.