Broadband microstrip branch-line coupler with defected ground structure

The design and measured performances of a broadband branch-line coupler are presented. The broadband coupler was designed by using a four-section branch line topology with a structure of the defected ground. Such a structure can make the impedance of the microstrip line much larger than that without defected structure, even using a normal PCB process. More than 231 Ω was easily achieved by such a defected structure. The measured performance of the broadband coupler agrees well with the results from simulation.