Ultra-wideband bandpass filter with sharp tuned notched band rejection based on CRLH transmission-line unit cell

Abstract

The proposed filter satisfies the Federal Communications Commission ultra-wideband (FCC-UWB) specifications and also creates and controls sharp rejection notch-bands within the filter’s passband in order to provide interference immunity from unwanted radio signals, such as wireless local area networks (WLAN) and worldwide interoperability for microwave access (WIMAX) that cohabit within the UWB spectrum. This filter is based on CRLH concept consisting of an asymmetric transmission line unit cell with a short circuited inductive stub to realize high performance in an operation band from 3.1 to 10.6 GHz with a very compact size of 16.4mm × 5.0 mm. The main advantage of the proposed filter is that four notch frequencies are tuned in the UWB frequency band. The notch frequencies of the filter can be changed by increasing the length of the coupling stub which is controlled by using switching matrix equipment (Mini Circuit) instead of PIN diodes. To validate the design theory, a microstrip UWB BPF with four notch bands centered at frequencies 6.18, 5.9, 5.7, and 5.5 GHz is designed and fabricated.