Quad-band bandstop filter using quad-section stepped impedance open stub resonator

A compact quad-band band stop filter (QBBSF) using quad-section stepped impedance open stub (QSSIOS) is proposed here. The filter is constructed with shunt QSSIOS and a series transmission line. The quad stopbands of QBBSF filters is controlled by varying the impedance of shunt QSSIOS and the passband performance is improved varying the impedance of series transmission line. The proposed filter is not only compact, but also has good performance in stopband as well as passband. The proposed filter working at center frequency of 4.5 GHz is fabricated, there is a good agreement between simulated and measured results.