Design methods for broadband 3dB branch-line and rat-race hybrids

Abstract

This paper considers band-broadening design methods for branch-line and rat-race hybrids such as 90- and 180-degree hybrids. For the 90-degree hybrid, utilizing external matching networks composed of coupled-transmission lines, broadband characteristics with a relative bandwidth of over 40% can be obtained for a 3dB hybrid designed for operation at 3GHz based on the equivalent admittance approach. For the 180-degree hybrid, a rat-race hybrid in which right-handed transmission lines are replaced with composite right-/left-handed transmission lines also realizes broadband characteristics. The validity of these design procedures has been demonstrated by electromagnetic simulations and experiments.