Design of compact triple-band branch-line coupler with three arbitrary operating frequencies

This paper proposes a triple-band branch-line coupler design by substituting the λ/4 transmission lines in the conventional branch-line coupler by II-shaped circuits composing of transmission lines, LC resonators and open stubs. The coupler is designed on a printed circuit board (PCB). Surface mount device (SMD) capacitors are used for the LC shunt resonators. The operated frequencies of this coupler are designed at the 0.9 GHz, 1.575 GHz, and 1.8 GHz. Simulated and measured results by full-wave simulators validate the design concept.