DESIGN AND IMPLEMENTATION OF COMPACT HYBRID FOUR-MODE BANDPASS FILTER WITH MULTI-TRANSMISSION ZEROS

This paper presents a novel compact microstrip hybrid four-mode bandpass fllter (BPF) with good selectivity and multi- transmission zeros. By adding an external resonator to a triple- mode stub-loaded resonator, four modes are generated in the desired passband and a hybrid four-mode BPF is implemented. Odd- and even-mode theory is introduced to investigate the mode characteristics of triple-mode resonator in detail. Circuit model and coupling matrix are built to further explain the proposed methodology. A microstrip BPF with central frequency of 3.4GHz for wireless communication was designed and fabricated. Three transmission zeros are obtained at 3.2GHz, 3.55GHz and 3.73GHz, which improve selectivity and out- of-band rejection of the fllter. The measured results of the fabricated fllter represent good in-band and sharp sideband characteristic, which match well with simulated results.