Design of the Modified Planar Tandem Couplers With a Wide Passband

Novel design equations and examples of the modified 3-dB microstrip tandem coupler are presented. In order to obtain a wide passband, couplers with a single pole/dual poles at the return loss are proposed. Compared to the conventional couplers such as Lange couplers and parallel coupled line couplers, high-impedance transmission lines and narrow coupling gaps are not required for the proposed microstrip coupler. In terms of measured results, there is a wide bandwidth of more than 70%. Moreover, good agreement between theoretical predication and measurement validates our proposed structure.