Dual-band microstrip bandstop filter using dual-mode loop resonator

A dual-band bandstop filter (DBBSF) with a dual-mode loop resonator is presented. In order to allow the DBBSF to exhibit high skirt selectivity and to generate a wide rejection bandwidth a capacitive coupled-line section is introduced. By properly controlling the length of the coupled-line section and the cross-coupled capacitor, more than two finite transmission zeros were inserted at the stopband and enhanced the rejection bandwidth.