Wideband open stub BPF for cognitive radio system applications

Abstract

In this paper, a compact wideband open stub bandpass filter (BPF) is designed, fabricated and characterised for cognitive radio system (CRS) application, which is an emerging technology in the wireless communication system. The designed BPF can be implemented to a front end of CRS system that can pass the desired signal rejecting all other signals and noise. We fabricated on Teflon substrate with dielectric constant of 2.54 and thickness of 0.54 mm and characterised using vector network analyser. The experimental results of wideband BPF are found in good agreement with simulated results, showing fractional bandwidth from 4.4-8.0 GHz (approximate to 59%), insertion loss (S-21) of 33.6 dB, and minimum return loss (S-11) of 0.10 dB at 6.2 GHz. The group delay of wide BPF is below 0.19 ns. The features of the design are size reduction, wideband, higher insertion loss, feasibility in implementing to CRS. The designed wide BPF occupied the size of 0.394 x 0.601 lambda g.