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A novel compact quintuple-mode stub-loaded resonator and ultrawideband (UWB) bandpass filter (BPF) are proposed in this letter. The proposed resonator can generate two odd modes and three even modes in the desired band. The odd-mode resonance frequencies are exclusively correlated to the modified triple-mode resonator; even-mode resonance frequencies can be flexibly controlled by the impedance-stepped open and short stub at its central plane, whereas the odd-mode ones are fixed. The open stubs in pairs at two sides of the low-impedance line are mainly applied to adjust the high resonant modes (fm4, fm5) into desired passband. The short stub can generate two transmission zeros near the lower and upper cutoff frequencies, leading to high rejection skirt. A quintuple-mode UWB filter is simulated, fabricated, and measured. The EM simulated and measured results are presented, and an excellent agreement is obtained.