Miniaturized Semi-Lumped UWB Bandpass Filter with Im- proved out-of-band performances

A miniaturized ultra wideband (UWB) bandpass filter with improved out-of band performances is presented in this paper. Based on the combination of low-pass and high-pass filters, the UWB filter is realized in a semilumped technology using microstrip transmission lines and surface mounted capacitors. In this paper, the filter design rules have been carried out. Furthermore, filters having a 3-dB fractional bandwidth of 142% centered at 0.77 GHz have been realized. Measurements in good agreement with simulations, show attractive properties of return loss (|S11|<-18 dB), insertion loss (<0.3 dB). Moreover, a technique adopting capacitively loaded stubs was used to extend the stopband till 8 times the center frequency.