In this paper, a novel ultra-wideband (UWB) bandpass filter (BPF) based on multiple-mode resonator (MMR) is presented. The structure of the proposed MMR constructed by a modified triple-mode stepped-impedance resonator (SIR) loaded with a T-shape stub. This stub loaded resonator can generate two more resonate modes and two transmission zeros (TZs) simultaneously. Five resonate modes of the proposed MMR are roughly allocated in the UWB pass band, as well as two TZs at the lower and upper cut-off frequencies of the passband, leading to sharp roll-off. Using aperture-backed interdigital-coupled lines for feeding, passband is realized, first harmonic resonate mode (sixth mode) suppressed by first TZ of the interdigital-coupled lines, and upper stopband extended. Resonant modes and TZs are discussed together. Finally, the proposed filter is fabricated and measured, and predicted results verified in measurement.
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