Design of the unequal power-divided dual-band coupler with coupled-line ring

The microstrip dual-band coupler with coupled-line ring has been provided. Within the proposed couplers, a coupled line with a half/quarter wavelength and two quarter-wavelength Schiffman phase shifters are adopted. The proposed couplers can not only be operated at two flexible frequencies with both 90° phase differences, but also provides the required output power ratio at the designed dual frequencies by the derived formulae. In order to verify the proposed design methodology, two experimental dual-band couplers are designed and fabricated.