Rat-race directional couplers operating in differential mode

In this paper, a novel approach for realization of rat race directional couplers is presented allowing for operation in a differential mode. The proposed couplers are analyzed in a two-mode structure and realized using two-conductor-over-ground transmission line technique. Moreover, bandwidth enhancement using phase inverter and miniaturization of the proposed differential-mode rat-race couplers have been investigated. The presented analysis has been confirmed by measurements of two exemplary manufactured circuits.