The design and fabrication of a high selectivity bandpass filter based on composite right/left-handed (CRLH) 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 1.55-dB insertion loss at the center frequency of 7 GHz. Two transmission zeros are located at 4.47 GHz and 9.03 GHz with -46.7 dB and -37.7 dB, respectively. Also, a wide rejection band from 8.29 to 14.5 GHz is obtained.