Novel Designed CSRRs and Its Application in Tunable Tri-Band Bandpass Filter Based on Fractal Geometry

In this paper, we propose and research a novel miniaturized composite right/left handed transmission line (CRLH TL) cell based on revised complementary split ring resonators (CSRRs) for the first time. Novel CRLH TL cell is demonstrated with lower transmission and reflection zeros from electrical and electromagnetic (EM) simulation results. Negative refractive index of CRLH effect is successfully demonstrated by the revised NRW retrieval method. Then based on this, a tri-band bandpass filter (BPF) is synthesized and fabricated by using the proposed CRLH TL cell (providing the primary GSM band) and Koch fractal-shaped microstrip line (ML) (generating the upper GPS and ISM bands). Our recent work has also found that open-circuit stub embedded in Koch-shaped ML can be optimized to adjust the ratio of the upper two bands, thus afford us additional flexibility in BPF design. Consistent result obtained from simulation and measurement is presented which have verified the design concept.