Design of dual-band filters utilizing new branch-line resonators

In this study, a new branch-line resonator is presented for dual-band filter design. By reducing one open stub of the conventional branch-line resonator, the filter structure will be simplified. Besides, since the external quality factor and center frequencies of two passbands can also be designed individually, the design procedure is therefore simplified. For demonstration, two dual-band filters have been designed and fabricated. The measured results are in good agreement with simulations.