Multiple-mode stub-loaded resonator with quadchannel diplexer and tri-band bandpass filter are presented and analyzed theoretically in this paper. The multi-mode stub-loaded resonator employs the basic structure of a triplemode resonator. Herein, the triple-mode resonator is modified by introducing a mid-coupled line between the odd-mode resonances to produce a quad-mode resonator. The proposed resonator is applied in the quad-channel diplexer design, composing of two independent dual-band bandpass filters. In turn, the triple-band bandpass filter based on a parallel quadmode and a dual-mode stub-loaded resonator is developed. To validate the performance of the proposed resonators, two experimental examples, including a quad-channel diplexer and a triple-band bandpass filter are fabricated and measured. Each of the designed circuits occupies small area, i.e. about 0.32λg×0.22λg and 0.18λg×0.20λg respectively. Good agreements between simulated and measured results are achieved.
