A compact coupled-line hairpin resonator is proposed and analyzed for designing a novel bandpass filter (BPF) in this letter. Compared with conventional stepped-impedance and stub-loaded resonator, the proposed resonator can produce three transmission zeros, which can be applied to achieve a wide and highly-attenuated upper stopband. To validate this attractive feature, a microstrip BPF is designed and fabricated with the center frequency at 2.4 GHz and a fractional bandwidth of 6%. Measured frequencies responses show a wider upper stopband up to 6.9 GHz (2.9f0) with insertion loss higher than 20 dB.
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