Millimeter-Wave Multilayer Ultrawideband Common-Mode Filters Using Defected Ground Structure

This article proposes two innovative millimeter-wave multilayer ultrawideband common-mode filters (CMFs). Microstrip lines and striplines are employed in CMFs to accomplish more comprehensive research. Common-mode (CM) suppression can be substantially strengthened by introducing a sandwich-like stack-up structure. The equivalent circuits expressed by the transmission line model are provided and analyzed. Analysis of electric/magnetic field is also given. For the proposed microstrip line CMF, a 13.04-GHz wide stopband response covering 17.91–30.95 GHz can be obtained. For the proposed stripline CMF, the 10-dB bandwidth can reach up to 20.12 GHz (17.39–37.51 GHz). Moreover, the differential-mode (DM) insertion loss of CMFs within 40 GHz is less than 3 dB. The proposed CMFs exhibit excellent DM matching level, ultrawide CM stopband bandwidth, low mode conversion level, and compact size.