Group Delay Investigation of Rat-Race Coupler Design With Tunable Power Dividing Ratio

This letter presents, for the first time, the theoretical and experimental investigation of the group delay characteristics of a rat-race coupler with variable power dividing ratio. By analytically study, the group delays associated with different transmission paths are found to be identical and can be made independent of the power dividing ratio by the proper design of the embedded networks. For validation, both simulated and measured results of a 1 GHz variable rat-race coupler implemented on microstrip are shown.