Asymmetric dual-passband coplanar waveguide filters using periodic composite right/left-handed and quarter-wavelength stubs

A novel dual-passband coplanar waveguide (CPW) filter periodically loaded with the composite right/left-handed (CRLH) short-circuited stubs and the quarter-wavelength open-circuited stubs in asymmetric configuration is presented. The unit-cell equivalent circuit of the periodic structure in conjunction with Floquet's theorem is employed to find the propagation characteristics of passband and stopband regions. Unlike the conventional quarter-wavelength transmission-line inverter suitable only for a narrow frequency range, the dual-band inverter is adopted in the dual-passband filter to achieve a better frequency response within two operating bands. The performance of the 2.4/5.8-GHz third-order CRLH CPW dual-passband filter with 52% and 23% bandwidths is measured and validated by full-wave simulation. Two arbitrary passband regions are presented and the stopband within the passbands can be controlled by varying the length of open-circuited stub, supporting the flexibility and compactness of the proposed dual-passband filter.