Impact of metallization layer structure on the performance of G-band branch-line couplers

Five different versions of grounded coplanar waveguide (GCPW) branch-line couplers on GaAs were EM simulated, processed and investigated for operation in G-band (140-220 GHz), based on different layer structures (including 2 or 3 metallization layers) and layouts. The best results have been obtained with the structures based on a continuous galvanic metal in the central conductor line and ohmic connections between top ground planes, reducing the insertion losses by 0.8 dB. A measured amplitude imbalance less than 0.5 dB from 160 to 200 GHz (22%), with a coupler insertion loss lower than 1.3 dB was achieved for a 3 metallization layer branch-line coupler.