Bandpass Filter with Wide Stopband Using Composite Right/Left Handed Transmission Line

Abstract This paper presents a wide-stopband bandpass filter (BPF) based on mixed coupling of the composite right/left handed transmission line (CRLH-TL). First the CRLH-TL resonator is introduced and analyzed. Then mixed coupling (Both electric coupling path and magnetic coupling path exist) of the novel resonator is explained. Based on the structural features of the CRLH-TL resonators, this coupling path can generate an additional transmission zero near passband without increasing the overall size of the filter. Then, good selectivity of the proposed BPF can be obtained. Meanwhile, in order to get a wide stopband, two open stubs are employed to suppress harmonic response of the CRLH-TL resonator. The filter is developed and analyzed based on microwave network theory and equivalent circuit method. The proposed BPF has been designed, fabricated, and measured. The measured results agree with the predicted ones closely.