Design of quad-band bandpass filter using open- and short-stub-loaded resonators

This letter presents a quad-band bandpass filter using open- and short-stub-loaded resonators. The proposed filter includes two sets of resonators. One set of resonators is embedded in the other and thus the filter is compact in size. The outer ones are open-stub-loaded resonators and the inner ones are short-stub-loaded resonators. The former one is designed to not only generate the second and the fourth passbands, but also feed the inner resonators. The latter one operates at the first and the third passbands. All the passband frequencies can be conveniently tuned to desirable values by altering the corresponding resonator dimensions. On each side of each passband, at least one transmission zero is realized, resulting in good skirt performance.