Novel Design of a Dual-Band Rat-Race Coupler with Large Power Division Ratio

This paper proposed a novel design of a compact dual-band rat-race coupler with large power division ratio. The closed-form design formulas are analytically derived using the even-odd-mode analysis. The proposed dual-band structure demonstrates compact size and ideal port isolation due to adding phase inverter to branches. The high impedance microstrip lines are the key for obtaining large power division and there is no need to insert additional shunt stubs for the dual-band operation. For verification, using the analytical design method, the power division ratio k=10 rat-race coupler operating at 1/6.16GHz is designed and fabricated. There are excellent agreement between the measured results and the simulated results.