A novel technique is explored to improve signal integrity in high-speed differential transmission lines by incorporating a Composite Right/Left-Handed Transmission Line (CRLH-TL) structure. This method aims to mitigate common-mode noise and signal integrity degradation caused by asymmetric bends in differential transmission lines. The primary source of common-mode noise in differential signaling is the phase difference due to length disparities between the inner and outer lines at bend discontinuities. By employing Double Negative (DNG) metamaterial exhibiting a reduced propagation constant, the phase difference can be effectively compensated. The proposed CRLH-TL compensation structure's effectiveness is validated through both frequency and time-domain simulations, demonstrating its proficiency to suppress common-mode noise across a broad frequency band.
Printed circuit boards (PCBs) driven by a connected feed cable are considered to be one of the main sources of the electromagnetic interference (EMI) from electronic devices. Effective methods for predicting and suppressing EMI over a broad band are required. In this paper, we newly focus on identifying the frequency response of EM radiation from a strip line structure driven by a connected feed cable. To provide basic considerations for the realization of methods for predicting the EM radiation from strip line structure driven by a feed cable, the characteristics of the EMI of test model PCB are investigated in this paper experimentally and by numerical modeling. Firstly, frequency responses of common-mode (CM) current and EM radiation from a PCB without the feed cable are discussed by FDTD modeling. It was demonstrated that SL and shield structures without a feed cable are effective in suppressing the EMI. Secondly, CM current on the feed cable attached to the PCB is studied experimentally and compared with FDTD modeling. Due to the additional displacement current path, "SL" structure driven by the feed cable is not effective in suppressing EMI. EMC design guideline commonly suggests that the strip line structure rather than microstrip line structure should be used in PCB structure. The results in this study indicate that "SL" and "Shield" cases yield resonances with high level peaks, due to the feed cable. This study successfully provides a basic model to effectively predict EM radiation from a stripline structure.
