A Compact Microstrip Low-Pass Filter Using D-CRLH Transmission Line with Ultra-Wide Stopband and High Selectivity

A novel structure of dual-composite right/lefthanded transmission line (D-CRLH TL) is proposed and analyzed in this paper. The simulated results show that there is a stopband between the first right-handed passband and the left-handed passband of the proposed D-CRLH TL. This stopband characteristic is applied to improve the electromagnetic performances of low-pass filter (LPF). A planar compact microstrip LPF with ultra-wide stopband (UWSB) and high selectivity is designed, fabricated and measured. The measured and simulated results are in good agreement with each other, indicating that this design method is effective and successful. The measured results show that the cut-off frequency of the LPF in this paper is 3.68 GHz, the stopband with insertion loss of more than 20 dB is from 3.84 GHz to 20.21 GHz (136.1 %), and the sharpness is 106.25 dB/GHz. Compared with the previous works of references, the LPF in this paper has less insertion loss, greater stop-bandwidth and better sharpness. Besides, this LPF also realizes a 73 % size reduction in comparison with the same work in reference [14].