Design of compact ultra-wideband (UWB) bandpass filter with notch band

This paper presents a compact band-notched ultrawideband (UWB) filter with a quasi-elliptic function response. This filter comprises of dual parallel centrally-loaded resonators with planar configuration. The two resonators operate at the lower and upper portions of the UWB passband. Inter-digital coupling structure is used not only to feed the signals to the resonators but also to generate a notch band at 5.8 GHz. The coupling strengths at various frequency ranges can be independently controlled. Two transmission zeros are generated close to the passband edges, exhibiting a quasi-elliptic function response, resulting in high skirt selectivity. The transmission zeros can be tuned individually to desirable frequencies which facilitate the designing procedure. An example filter is implemented and the results are presented to verify the proposed design.