Coplanar to microstrip transitions for on‐wafer measurements

Two types of via‐free coplanar line to microstrip transitions are designed and tested for on‐wafer measurements. The transitions are designed to fit coplanar ground‐signal‐ground probes. They are taper transitions with capacitive ground patches and radial stub transitions. Both structures are easy implemented and exhibit wideband transmission. The performance of the optimized taper transition is among the best demonstrated in terms of a return loss of less than −20 dB from 5 to 15.5 GHz; this is even superior to the radial stub designs. Design information is given, which is based on full‐wave simulations for the taper transition, and analytical formulations for the radial stub. The increasing bandwidth with increased angle of the radial stub is observed. The transition structures and design guidelines addressed can be used for on‐wafer measurements of a wide range of microstrip circuits.