A Lumped Coplanar to Microstrip Transition Model for De-Embedding S-Parameters Measured on GAAS Wafers

Currently most microwave measurements on GaAs wafers are made using RF probes which are calibrated to the probe tips. When a microstrip circuit or device needs to be measured, errors are introduced as a result of the transition from the coplanar probe tips to the microstrip line. In this paper an equivalent circuit of the transition to microstrip is presented. Knowing the characteristics of this transition, the S-parameters of monolithic microstrip circuits can be de-embedded from measured data. Comparisons of measured, theoretical, and de-embedded electrical characteristics are shown up to 26 GHz.