This letter presents a compact dual-band branch-line coupler. Explicit design formulas of the three-branch-line coupler (3-BLC) are derived and useful design curves are given. The equivalent dual transmission lines structure is used to decrease the dimension, and also the partial branch lines are folded to further miniaturize the design. The proposed dual-band (2.45 and 5.8 GHz) coupler has a compact size with 57.6% size reduction compared with the conventional circuit. The measured and simulated results are in good agreement with each other.
2017 by The Institute of Electronics, Information and Communication Engineers