A novel and compact ultra wideband (UWB) bandpass filter (BPF) with two transmission zeros near both passband edges of lower and higher frequency is proposed by using a new structure of fork-formresonators. The fork-formresonator generates a attenuation pole at the higher passband edge, lower insertion loss, wider bandwidth and compacter dimension, as compared with the traditional parallel unilateral-coupled resonator. A microstrip bandpass filter cascaded by two stages fork-formresonators with a 3-dB fractional bandwidth of 128% (from1.0 GHz to 4.6 GHz) is designed, fabricated, and tested. The measured characteristics of the filter agree with the theoretical simulations, and the measured results show good specifications which are very low insertion loss 0.5±0.3 dB within the passband and good return loss less than −15 dB from1.5 GHz to 4.0 GHz, respectively.
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