Measurements of impedance above 110 GHz

Measurements of impedance above 110 GHz are not as easy as similar measurements made below this frequency. One reason is that the range of commercial measurement equipment falls dramatically above 110 GHz and another is the high attenuation in most conventional transmission lines. Other reasons are the poor repeatability of connectors and the lack of good standard impedances above 110 GHz. All these reasons are present when attempting to measure on-wafer circuits. This paper will include a brief overview of the present state of the art above 110 GHz and then focus on the author's own work measuring coplanar waveguide impedances at 140 GHz.