A dual-band bandpass filter using a transversal-interference multimode resonator

A dual-band bandpass filter using a transversal-interference multimode resonator is proposed. The resonator is composed of a flatten ring resonator attached with two open-circuited stubs. By properly selecting the connecting position between the stubs and a ring, the two pairs of resonant modes can be grouped to make up the dual-passband response, and they can be further separated with virtue of two transmission zeros between them. By changing the length and the off-center position of these two stubs, both of dual passbands can be flexibly adjusted in terms of their central frequencies and bandwidths. In final, a dual-band filter with central frequencies at 3.5/5.4 GHz is designed and fabricated. The measured results are found in good agreement with the predicted ones.