Balanced-to-unbalanced filtering power divider using ring resonators

A novel balanced-to-unbalanced filtering power divider using ring resonators is proposed. Due to the symmetry of the circuit model, even/odd-mode analysis method is applied to deduce the design equations at the operating frequency. The ring resonators can bring two transmission zeros in each side of the passband for differential-mode, which can improve frequency selectivity and out-of-band suppression. A fabricated prototype (εr = 2.65, h = 1 mm, tan δ = 0.003) with 4-dB bandwidth of 12.5% is designed and measured to prove the proposed methods.