A wideband common-mode suppression filter using enhanced coupled defected ground structure

In this paper, we propose a wideband common-mode suppression filter for high-speed differential signals. The proposed design is realized by using only two enhanced coupled C-shaped defected ground structures (DGSs) with a long bridge to achieve the wideband common-mode noise suppression. The equivalent circuit model of two coupled LC resonators is also established with good agreement to the full-wave simulation and measurement results. A sample board is designed and fabricated on a printed circuit board (PCB) with FR4 substrate. It is proved that the differential-mode insertion loss is within -3 dB from DC to 12 GHz. Common-mode noise can be reduced over 10 dB from 3.7 GHz to 10.8 GHz in the frequency domain, and approximately 42% of amplitude in the time domain. Moreover, the fractional bandwidth of the stopband can reach 98%, and the filter size is only 0.3 λg × 0.3 λg, where λg is the wavelength of the stopband central frequency. To our knowledge, this is the first common-mode filter using an enhanced coupled mechanism for the high-speed signals to extend the stopband, and it is also a simple geometric structure with the largest fractional bandwidth and the most compact size on a PCB.