Wide bandwidth arbitrary phase difference branch line coupler

As a conventional branch line coupler (BLC) is limited toa phase difference of 90°, different phases have typically been realized by cascading additional phase-shifters,which inevitably increase the circuit size. This articlepresents a BLC capable of achieving a combined widebandwidth and arbitrary phase difference. This is achievedby inserting a phase compensation network directly ineach of the series branch lines, which effectively modifiesthe electrical lengths. A prototype 60°/–120° coupler hasbeen fabricated and experimentally characterized toachieve a 0.5-dB magnitude imbalance, 5° phase stability,return loss better than 215 dB, and isolation better than214 dB from 2.3 to 3.5 GHz.