A quad-band bandpass filter utilising stub-loaded resonators is presented. The symmetric resonator is analysed by using even-mode and odd-mode technique. The resonator provides one transmission zero and four transmission poles for the four passbands. With the multi-line input/output coupling configuration and multipath propagation between the meandering resonators, one can generate two additional transmission zeros to improve the suppression among passbands and achieve a high design freedom for the four passbands.
