A novel UWB bandpass filter and its application to UWB pulse generation

This paper presented an ultra-wideband (UWB) bandpass filter using broadside-coupled microstrip-coplanar waveguide structure. The filter consists of a microstrip line coupled to a coplanar waveguide (CPW) that was fabricated on the ground of the microstrip line. The proposed filter has been simulated, fabricated and measured for UWB system. The measured results of a 3-section filter demonstrated the best UWB performance around the world: bandwidth from 3.0 GHz to 10.63 GHz (@-10 dB); insertion loss at central frequency about 0.32 dB and very flat over the whole band; group delay, which is important to an impulse radio UWB system, about 0.42 ns over the most central band, and less than 0.95 ns over the whole band. The filter also exhibited a good performance outside the band, both at low frequency end (to meet FCC limit) and high frequency end higher than 18GHz with insertion loss better than 30 dB. The developed bandpass filter has been successfully applied to the UWB pulse generation. The experimental results demonstrated that a step-like negative pulse with less than 5 ps falltime, generated from a pulse generator, was reshaped through the filter as a Gaussian doublet-like UWB pulse.