Design of Planar Baluns With Filtering Response Using Coupled Line Sections

Two types of planar baluns have been proposed in this letter. Coupled line sections are used for balanced responses as well as impedance match to avoid large coupling coefficient. Due to asymmetric topologies, performances are obtained by calculating S-parameters directly while simpler even–odd mode analysis is also feasible with an introduced virtual port. For validation, two prototypes are fabricated at 3.5 GHz. Simulated and measured results show that the proposed baluns have low in-band imbalance and good filtering response.