Low-loss Broadband GSG for Sub-THz Applications in InP Technology

A low-loss, broadband ground-signal-ground (GSG) archi-tecture based on indium phosphide (InP) technology has been fabricated with a compact one-port dimension of 0.35 × 0.075 mm^2. This innovative architecture employs a ground shield to eliminate the high-loss signal path typical-ly caused by the parasitic substrate resistor. To further re-duce the impact of parasitic capacitance between the top and bottom layers, an open-window design has been introduced beneath the signal pad (S-pad). Measured results for the back-to-back GSG configuration indicate an insertion loss (IL) of less than 0.6 dB and a return loss coefficient greater than 10 dB across a bandwidth extending from DC to 170 GHz. These results closely align with the simulated data, showing only minor differences. The improved design minimizes substrate coupling through the signal pad, lead-ing to better noise characterization of devices and making it particularly well-suited for sub-terahertz (sub-THz, >100 GHz) applications.