Impact of Substrate Modes on mTRL-Calibrated CPW Measurements in G Band

On-wafer measurements at microwave and mmwave frequencies require reliable calibration processes to deduct unwanted effects such as the impact of probe, the wafer environment, and the instrumentation equipment itself. However, with increasing frequencies the calibrated results become more and more sensitive to parasitic effects such as radiation, multimode propagation, and substrate modes. This paper investigates their influence when using a typical coplanar waveguide (CPW) calibration substrate at G band. The goal of this paper is to clarify the role of substrate modes and to quantify how they affect multiline Thru-Reflect Line (mTRL) calibration.