Highly Miniaturized and Wideband 3-dB Quadrature Hybrid Using Slow-Wave Coupled Line

A novel highly miniaturized wideband quadrature hybrid using slow-wave technology is proposed in this paper. In order to reduce the size of conventional branch-line/coupled-line couplers, a unique structure is utilized based on two layers of crossing strips with densely interconnecting vias. This structure makes full use of the electrical coupling and magnetic coupling in the slow-wave structure, and enhances the mutual inductance effect between parallel vias, which successfully leads to enhanced coupling strength that enabling the wideband 3-dB quadrature hybrid. Importantly, 99.4% of size reduction has been achieved as compared to conventional three-section branch-line counterpart while maintaining an equally good performance. The achieved relative planar area is only 0.003A
²
, which is orders-of-magnitude improvement over state-of-the-art.