Accuracy enhancement of the Whispering Gallery mode resonator method using substrates with identical sizes to measure the conductivity and the complex permittivity

We have enhanced the WG mode resonator method by using the substrates with the same thickness to evaluate the conductivity and the complex permittivity in the same frequency band. Using the proposed technique we investigate frequency dependencies of PTFE substrate with three types of copper-foils in 55 to 70 GHz band. In the conventional measurements, the conductivity of electrodeposited copper foils is 56% of the value of the international standard annealed copper. However when we used substrates with the same thickness for the measurement the conductivity of electrodeposited copper foil is 35%.