Wideband CRLH-transmission line bandstop filter

A new compact broadband bandstop filter using composite right/left handed transmission line (CRLH-TL) is presented. The filter is designed based on a signal interference mechanism. The CRLH-TL is used to substitute the three-quarter-wavelength transmission line, thus the total size is largely reduced. A meandered slotline is etched on the ground plane below the interdigital capacitor to improve the upper passband performance. A bandstop filter with about 70% fractional bandwidth (FBW) at 3 GHz has been designed and fabricated. The size of the fabricated filter is 0.23 λ_g × 0.084 λ_g.