Dual-band branch line coupler with large power division ratios

Abstract

Design of dual-band branch line couplers with large power division ratios is proposed. Large power division ratio is achieved by replacing the conventional branch lines with shorted parallel-coupled line sections. For dual-band operation, open stubs are attached to the branch lines at the connecting nodes in the circuit. Design equations incorporating arbitrary power division ratios are formulated by imitating the quarter-wave branch-lines at the two designated frequencies with different characteristic impedances. A microstrip coupler operating at 2.45/5.2 GHz with 20/15 dB power division ratios is designed, fabricated and tested to validate the theory. Good agreement is obtained between experiment and simulation results.