An Improved UWB Bandpass Filter with a Notch-band Based on Asymmetric Parallel-coupled Line with Compact Size

This letter presents an improved UWB bandpass filter with sharp selectivity and a notch-band. Its fundamental structure is mainly based on a half-wavelength resonator using asymmetric parallel-coupled line. A center-tapped short-stub is connected at the symmetrical plane of the filter. As a result, two transmission zeros at the lower and upper passband / stopband edges are obtained. Moreover, one open parallel-coupled line is introduced to achieve a notch-band. Measured results indicate that the proposed filter has achieved a bandwidth of 110.6% from 3.05 to 10.6 GHz with a notch-band at 8.5 GHz. In addition, this filter can offer some other advantages such as sharp roll-off and compact size (0.63λ
_g
× 0.33λ
_g
), which make it attractive for the practical applications in UWB systems.