A Wideband Common-Mode Suppression Filter With Compact-Defected Ground Structure Pattern

A complementary-defected ground structure (DGS) common stopband filter is proposed. The filter uses two kinds of DGS patterns: a Π-shaped DGS pattern is used in both sides of the filter and a button-headed H-shaped DGS pattern is adopted at the middle of the filter. The filter utilizes the mutual inductance and mutual capacitance that exists among the DGS patterns to improve the in-band gain-flatness of the filter, which is useful to broaden the bandwidth and improve the rejection ratio in the low cutoff frequency. The simulated and measured results show that the differential signal under the DGS filter is nearly intact and the common-mode noise can be reduced by 15 dB from 3.2 to 12.4 GHz. The area of the filter is only 10 mm × 10 mm. The fractional bandwidth of the stopband can reach 118%.