The effect of slotline on the bandwidth performance enhancement of branch line coupler

This paper proposes a new branch-line coupler with slots operates from 3.5 GHz to 4.7 GHz frequency band. The proposed design concerns the addition of slotline at the ground plane underneath the right and left branch of the coupler. The design and parametric study of the proposed coupler are performed using CST Microwave Studio. The length and width of slots are varied to study the wideband performance of the coupler. The proposed coupler has significantly improved bandwidth performance up to three times wider than the conventional coupler with good 3 dB coupling, return loss and isolation.