Errors in on-wafer measurements due to multimode propagation

We study for the first time effects of multimode propagation in on-wafer conductor-backed coplanar waveguide (CB-CPW) standards applied to the vector network analyzer (VNA) calibration. We consider a two-step calibration approach that relies on a preliminary system calibration using standards on a manufacturer's precision substrate and then additional measurements made on custom on-wafer standards to account for differences in the probe-tip-to-line geometry and substrate permittivity. We simulate multimode effects in the transition between an on-wafer probe and the CB-CPW using a 3D electromagnetic (EM) numerical analysis and from that we determine errors in the S-parameters measurements, which result from the multimode propagation. We show that they may severely affect the measurements when calibration standards are lengthy.