Compact broadband multi-zero bandpass filters (BPFs) demonstrate superior performance including wide bandwidth, high selectivity, and sharp out-of-band rejection. By employing multi-mode resonance and hybrid structure designs, these filters enhance nonlinear response and interference suppression, achieving ultra-wideband operation (>100% relative bandwidth) while maintaining excellent stopband performance. This paper presents a compact broadband bandpass filter design with multiple transmission zeros based on a parallel-coupled line structure. The proposed design employs a novel cascaded compact coupled-line structure with a wide stopband, achieving multiple transmission zeros while maintaining broadband characteristics, thereby effectively extending the stopband bandwidth. The research includes: analysis of the filter's resonance mechanism and transmission zero characteristics, parameter sensitivity study, electromagnetic simulation modeling, and optimization. The final measured results demonstrate a return loss better than 10 dB within the 3.5 GHz ~ 6.5 GHz frequency band, an insertion loss of approximately 0.29 dB at the center frequency, a 3-dB fractional bandwidth (FBW) of 91.2%, and an out-of-band suppression of 20 dB at four times the center frequency (20 GHz).
Key words
ultra-wideband /
phase shifter /
filter /
miniaturization /
parallel-coupled line /
wide stop-band
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