Effects of ground-to-ground connections on coplanar waveguide calibration standards for terahertz on-wafer measurements

Paper in proceeding, 2025

On-wafer measurements at terahertz frequencies remain challenging; discontinuities or asymmetries in coplanar waveguide (CPW) transmission lines can excite higher-order modes, leading to inaccurate calibration. In this work, we study the effects of two types of odd-mode suppression structures for CPW lines and compare them with a conventional design. The waveguides were fabricated on a semi-insulating InP substrate, and measurements were performed between 325 GHz to 1100 GHz. We show that by connecting the ground planes using air bridges, the accuracy of the calibration is improved. The probable reason is the suppression of the odd mode; however, secondary effects, such as crosstalk, require further investigation.