A Novel Compact Broadband Two-Section Branchline Coupler with Circular-Coupled Lines

This paper introduces a novel compact broadband two-section branch-line coupler. In traditional branch-line coupler designs, researchers frequently faced substantial hurdles. They grappled with large-scale dimensions that restricted their applications in space-constrained scenarios, and impedance matching problems led to sub optimal performance. The presented coupler features an ingeniously constructed external matching network from improved circular coupled lines. The use of these circular lines is a key innovation, reducing the overall size by 21.5% in contrast to their traditional counterparts. Additionally, a rectangular defected ground structure (DGS) is precisely etched into the ground plane beneath the three-branch line directional coupler structure. This process significantly improves the characteristic impedance of the branch lines. As a result, this innovative design impressively achieves a measured bandwidth of 46.8% at a center frequency of 2.2 GHz. By harnessing the distinct properties of circular coupled lines and DGS, our proposed coupler effectively overcomes these longstanding limitations, presenting a more efficient and compact solution for diverse applications such as 5 G communication systems, wireless sensor networks, and satellite communication devices.