Miniaturized Quarter-Wavelength Resonator for Common-Mode Filter Based on Pattern Ground Structure

Two miniaturized methods for quarter-wavelength resonator of common-mode filter (CMF) based on pattern ground structure (PGS) are proposed. By the proposed symmetric structure, the size of CMF can be reduced by 33.7 ^% compared to the conventional work with the straight quarter-wavelength open stub. To achieve further size reduction, the asymmetric structure is also investigated. By utilizing asymmetric PGS, the size of CMF can be significantly reduced by 61.1 % compared to the conventional work. Moreover, the two-stage asymmetric PGS provides the wider common-mode (CM) stopband bandwidth and it is still smaller than conventional work. The differential mode insertion loss can be also improved owing to the small size of the proposed CMFs.