A Comparative Study between Via-Hole and Via-Free Grounded Coplanar Waveguide to Microstrip Transitions on Thin Polymer Substrate

A comparative study between via-holed and via-free back-to-back GCPW-MS-GCPW (Grounded Coplanar Waveguide-Microstrip lines) transitions is reported in this paper. According to simulation results, both via-holed and via-free transitions on commercial benzocyclobutene polymer 20 mu m film show a bandwidth over 57GHz. Bandwidth of optimized via-holed transitions increases with the via-hole diameter, up to 75GHz with 300 mu m via-hole diameter. The via-hole free transition achieves experimentally an ultrabroadband from 2 GHz to 78 GHz with an insertion loss of only 0.5 dB thanks to the copper metallization thickness of 2 mu m. In addition, these measurement results are in perfect agreement with the simulation results. These via-free and via-holes transitions are very useful and requested in component packaging, on-wafer measurements of microstrip based microwave integrated circuits, and also the interconnections in hybrid circuits including both microstrip and coplanar structures.