Complex permittivity measurements of a PTFE substrate in W band by the cut-off circular waveguide method

The complex permittivity measurements of a PTFE in the direction tangential to a plate are performed to investigate accuracy of a cut-off circular waveguide method in W band by using four resonators. Moreover, the novel 100GHz grooved circular empty cavities and newly developed excitation cable are introduced. The fabrication deviation of these cavities is extremely small and the high relative conductivity over 90% is achieved. As a result, the PTFE has relative permittivity ϵ_r of 2.05±0.01 and low loss tangent tanδ of (2.7±0.2)×10^-4 around 84GHz. And also, the measurement precision of the method in W band is 0.6% for the relative permittivity ϵ_r ≅ 2 and 5% for the loss tangent tanδ ≅ 10^-4.