Metamaterial transmission line based bandstop and bandpass filter designs using broadband phase cancellation

This paper presents a methodology of designing a microwave bandstop filter and a bandpass filter by using a Composite Right/Left Handed transmission line (CRLH-TL) as part of a transversal filter. The CRLH-TL can be engineered to have specific phase slope and phase offset. Connecting the CRLH-TL and the conventional microstrip delay line at both input and output can establish a transversal filter where the signal merging at the output has broadband out of phase characteristics. Therefore, the bandstop filter can be created with signal rejection over a wide frequency range. The measured 3dB bandwidth of the bandstop filter is 130% and the minimum insertion loss at the next passband is -1.7dB. In addition, based on the bandstop filter a bandpass filter with a wide signal rejection range is developed by creating a frequency dependent defect in one branch of the bandstop filter. This is implemented by either attaching a microstrip open stub or capacitively coupling a microstrip resonator to the microstrip delay line. The 3dB passband bandwidth and the minimum insertion loss are 18%, -1.5dB and 8%, -2dB corresponding to the open stub and the resonator scheme, respectively.