Low-loss broadband (DC to 220 GHz) S-CPW to S-CPS transition for S-CPS coplanar probing

The practical issue of probing coplanar stripline (CPS) structures is addressed in this Letter. A compact slow-wave coplanar waveguide (S-CPW) to slow-wave CPS (S-CPS) transition was designed and fabricated in a 55 nm BiCMOS process of STMicroelectronics. The signal strips of the slow-wave CPW and slow-wave CPS have been directly connected while the ground strips have been tied together through combination of transmission lines laid out on the top metal layer of the back-end-of-line of the technology. Thanks to its flexibility, the proposed transition can be resized to match with a wide range of slow-wave CPS slot. Tested from DC to 220 GHz, the back-to-back transition structure showed insertion loss lower than 1.4 dB and return loss better than 15 dB, respectively. To the best of author's knowledge, it is the first integrated slow-wave CPW/CPS transition introduced within the mentioned mm-wave band.