Design of UWB filter with steep rejection slope based on fractal-shaped Composite Right/Left Handed Transmission Line

The application of traditional Composite Right/Left Handed Transmission Line based on micro-strip slit and Complementary Split Ring Resonators (CSRRs) is limited because of its narrow bandwidth and high insertion loss in passband. In order to solve these problems, microstrip slit based on Minkowski fractal is used to broad the bandwidth, and bilateral stubs are loaded to improve band-stop characteristic at the high edge of passband in this article. The influence of dimension parameters of structure on transmission characteristics is analyzed, and dispersion curve and equivalent circuit model are gained according to S-parameters. Finally, a type of Ultra-Wide-Band (UWB) Filter is designed by using the proposed CRLH. The designed filter exhibits lower insertion loss (less than 0.8dB) in the pass-band, wider bandwidth from 2.1GHz to 9GHz (relative bandwidth 124.3%) with a compact size and a rejection level higher than 20dB was obtained at the stop-band from 9.5GHz to 12GHz. Results obtained from simulation, circuit model and measurement show good agreement which indicate that the design of the proposed filter is effective.