A Compact Dual-Band Planar Branch-Line Coupler

A novel branch-line coupler which can operate at two frequencies is presented in this paper. The proposed planar topology, which is different from the conventional one, is analyzed and designed. The new coupler maintains not only compact but also dual-band characteristics. The length of the proposed stepped-impedance lines can be adjusted flexible according to the required operation frequency. In order to verify the method, a dual-band micro-strip coupler operating at 0.9 and 2.1 GHz is fabricated and measured. The simulated and measured results show good agreements.