High selectivity microstrip bandpass filter using feedback CRLH-TL unit cell

A new and simple approach to design high selectivity microstrip bandpass filter (BPF) is reported. Based on the signal interference concept, the selectivity of a BPF using composite right/left handed transmission line (CRLH TL) unit cell is significantly improved. Thus, by employing a single coupled line section and CRLH TL unit cell in the feedback, a bandpass filter with high selectivity, multiple transmission zeros (TZs) within the upper stopband and low insertion loss can be realized. The simulation results show that the proposed BPF has a fractional bandwidth of 8% centred at 2.4 GHz with high roll-off rate of 300 dB/GHz.