A tapped stub-based compact balun

A generalized balun structure with a single stub is presented in this paper. The balun is designed based on a four-port device with one port set to be open-circuited. Even-odd mode method is applied to analyze its performance. The derived design equations show that multiple sets of solutions are available for the proposed balun. Therefore, it is highly flexible for practical implementations. To validate the design theory, a prototype balun working at 2.4 GHz has been designed, fabricated and measured. Good agreement between the simulation and measurement has been achieved.