Bandpass filters with improved selectivity based on dual-mode ring resonators

Abstract

Two novel micro strip band pass filters with improved selectivity based on dual-mode ring resonators are proposed. Tow and four transmission zeros close to the pass band are realized to improve the selectivity for the pass band. Sixth-order pas band is realized with two open/shorted stubs and a dual-mode ring resonator. The transmission zeros near the passband can be adjusted conveniently by changing the characteristic impedances of the coupled lines. For demonstration, two planar band pass filters (3-dB bandwidths 20.9%, 20.2%) are designed and fabricated.