Compact Power Divider and Balun With Quadruplet Filtering Responses

A power divider and a balun with bandpass characteristics are designed and realized with integration of quadruplet filters. Quarter-wave resonators are used as building blocks of the quadruplets so that the entire circuits are compact in size. With the aid of coupling matrix synthesis, transmission zeros can be created at designated positions on both sides of the passband at both outputs. Before the layouts of these two three-port circuits are finalized, special attention is paid in electromagnetic simulation to the differential phase responses of the two outputs. Two experimental circuits centred at 2.5 GHz are fabricated and measured. Good agreement between simulation and measurement results validates the design concept.