###### Abstract  
A novel wideband common-mode (CM) suppression filter is proposed for high-speed transmission. The filter is embedded in 3 10 mm \(\times\) 10 mm layers of a printed circuit board (PCB) that combines a mushroom structure and a defected corrugated reference plane structure (MDCRP). Using the novel MDCRP structure generates more resonance frequencies in the CM current return path. This generates a wider CM noise suppression performance. We used a simulation method to obtain the best geometric parameters for the MDCRP structure. The experimental results proved that the full-wave simulation results were consistent with the actual measurement results. This novel filter shows good signal integrity according to actual measurements, and the insertion loss can be kept to less than \(-2.306\) dB from DC to 21 GHz in differential mode (DM). The CM noise can be suppressed by over \(-10\) dB from 5.09 GHz to 20.62 GHz. The fractional bandwidth is 120.8%, and the CM noise improves by 64.5%. An eye diagram proves that the filter can support a 20 Gb/s transmission rate with complete differential signal transmission capability. The MDCRP structure filter can support HDMI 2.0, PCI Express 4.0, USB 3.2, and SATA Express. Therefore, the filter meets current computer and server system products' design needs. common-mode noise; differential signal; electromagnetic interference; mushroom structure; signal integrity +
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thickness, and via design to reduce reflection and signal attenuation [4]. In a microstrip configuration, the high-frequency return current follows the path of least inductance back to the source. In the case of plane splitting or layer transitions to different references, the return current is forced to deviate from the ideal path. Non-ideal return paths can also generate CM currents, adding to EMI problems [5]. Bending and asymmetrical traces due to component arrangement in dense PCB layouts cause unwanted CM noise and signal integrity issues, which can lead to severe EMI issues [6]. Many CM filter designs involving defected ground structure (DGS) and mushroom-like structures have been published, which were to solve the related CM noise problems. In these DGS structural papers, a double-slit complementary split ring resonator (S-DBSCRR) structure filter has etched a slot to support the highest rejection frequency of 4.07 GHz [7]. A DGS structure filter used 2 enhanced coupled C-shapes to achieve the highest suppression frequency of 10.8 GHz [8]. Adding 3 varactor-loaded into a DGS structure filter achieved the highest suppression frequency of 8.1 GHz [9]. Using 5 DGS units to become a dual-resonant function filter achieved the highest suppression frequency of 4.6 GHz [10]. These DGS structures have been studied in the literature, and they can only support a suppression frequency of up to 10.8 GHz, so they cannot support today's computer design requirements. Mushroom-like structures with different structural changes and noise suppression capabilities have been studied in the literature. For example, a 4-mushroom structure for a filter using negative permittivity metamaterials achieved the highest suppression frequency of 7.1 GHz [11]. Using a pair of meandered lines and a mushroom-like structure filter achieved the highest rejection frequency of 5.2 GHz [12]. The filter uses a quarter-wavelength resonator to support the highest suppression frequency of 10.1 GHz [13]. A filter that combined a pair of meandered lines and multi-layer mushroom-like structures achieved the highest rejection frequency of 13.41 GHz [14]. A combination of a serpentine transmission line and a ring structure filter achieved the highest suppression frequency of 7.87 GHz [15]. The periodically corrugated reference plane (PCRP)-structured filter achieved the highest rejection frequency of 10.4 GHz [16].