A low insertion loss and high selectivity uwb bandpass filter using composite right/left-handed material

A novel bandpass filter (BPF) based on the composite right/left-handed (CRLH) material and 0° feeding structure is proposed. With multiple unit-cells cascaded, the new section comprises the series interdigital capacitors and the shunt short-circuited stub inductors in the symmetric configuration. The circuit is designed to be unbalanced, a tunable gap between left handed and right handed modes in the β - ω diagram can control out of band performance. With careful design, a bandpass filter with wide rejection band can be achieved. Furthermore, by using the 0° feeding associated structure, two extra transmission zeros are created just outside the intended passband. Finally, a three cells bandpass filter has been designed and fabricated with 1.1 dB insertion loss at the center frequency of 4.2 GHz. Two transmission zeros are located at 2.95 GHz and 6.18 GHz with attenuations of -44.1 dB and -37.3 dB, respectively. Also, a wide rejection band from 5.4 to 9 GHz is obtained.