An ultra-wideband(UWB) bandpass filter using broadside-coupled structure and shunt stub with chip capacitor

This paper presents an ultra- wideband (UWB) bandpass filter using broadside- coupled structure and combining shunt stub with chip capacitor to improve the out-band performance of the filter, particularly at the low frequency end. The measured results show that combining the filter and the shunt stub circuit produces an UWB bandpass filter with good performance, including the low insertion loss about 0.46 dB and low group delay about 0.26 ns at the center of the passband and very flat over the whole passband, and less than -10 dB reflection. The implemented attenuation poles, particularly at the low frequency end, dramatically improves the out-band performance, leading the filter satisfy the FCC´s spectrum mask not only for indoor but also for outdoor applications. These poles improved also the skirt performance at both filter edges. The developed UWB bandpass filter has a compact size of 4 cm times 1.5 cm.