Design of a broadband microstrip 180° hybrid

The 180° hybrid is a fundamental component in microwave circuit. It's inherently a narrow-band structure. This paper presents the design and performance of a broadband microstrip 180° hybrid operating from 3 to 5 GHz. The hybrid is composed of a power divider and a marchand balun. By designing a new three coupled lines marchand balun structure instead of conventional narrowband balun, the hybrid achieves a broadband phase shifting and power splitting while maintaining perfect matching and output isolation. Simulated and measured results show that the designed 180° hybrid obtains good performances including low return loss level, low amplitude and phase difference between output ports and high isolation. Simple equations based on the scattering matrix are also presented in this paper.