Verification of Reference Impedance from Common On-Wafer Calibrations on Commercial Calibration Substrates

This paper compares the reference impedance (Z
ref
) of common on-wafer calibrations (SOLT, LRRM, multi-line TRL) on a commercial calibration substrate. First, a method to extract Z
ref
of a calibration, based on the calibration comparison technique, is presented. Its application shows that lumped-standard calibrations have comparable Z
ref
up to ~40-50 GHz but require accurate lumped standards characterization, and LRRM Z
ref
is demonstrated to be particularly sensitive to probe misplacement on Thru and Load standards. It therefore confirms mTRL as reference calibration. However, measurements of two commercial calibration substrates have shown that even mTRL Z
ref
suffers from systematic errors linked to violation of the assumptions G’ = 0 and frequency-independent
$C$
’ line terms used to compute the line characteristic impedance.