Influence of microstrip probe pad design on planar measurements using on-wafer probes

This publication refers to work previously published by the authors at ISAP 2014. There, it has been shown how measurements with an on-wafer probe on planar transmission lines up to 67 GHz can be used for the determination of the transmission line´s substrate permittivity. Especially the microstrip probe pad on the substrate, which represents the probe-microstrip interface, has shown to be of significant influence on the measurement data, which allowed measurements up to only 25 GHz. The work presented in this paper gives measurement data with a doubled frequency limit of 50 GHz. Additionally, different sources of interference such as coupling, higher modes and probe pad design are discussed. An example for a broadband transition from on-wafer probe to microstrip is shown, which can be used for on-wafer or PCB antenna measurements up to 200 GHz. Finally, design rules on how to avoid the deteriorating effect on measurement data are given.