Analysis of errors in on-wafer measurements due to multimode propagation in CB-CPW

We study for the first time errors in on-wafer scattering parameter measurements caused by the parasitic microstrip-like mode propagation in conductor-backed coplanar waveguide (CB-CPW). We determine upper bound for these errors for typical CPW devices such as a matched load, an open circuit, and a transmission line section. To this end, we develop an electromagnetic-simulations-based multimode three-port model for the transition between an air-coplanar probe and the CB-CPW. Subsequently, we apply this model to examine errors in the device S parameters de-embedded from measurements affected by the parasitic MSL mode. Our analysis demonstrates that the multimode propagation in CB-CPW may significantly deteriorate the S-parameters measured on wafer.