Near-Field Coupling Analysis of Flexible Printed Circuit Boards

Flexible printed circuit boards (FPCB) can provide more circuit design solutions for the miniaturization of electronic devices due to their small size, lightweight, and flexibility for bending. However, RF interference from RF antennas or other radiation sources may lead to signal integrity issues in FPCB signal transmission with the increase in transmission rate. To address this issue, a method based on the reciprocity theorem is proposed for rapidly estimating the near-field coupling between two single-port devices on an FPCB under bending conditions. Three different cases for the FPCB, i.e., no bending, bending outside the victim transmission line (TL), and bending across the victim TL, are analyzed to characterize the near-field coupling by deriving the expressions of the scattering parameters. Moreover, the bending angle, rotating angle, bending position, and bending diameter of FPCB are further analyzed for their impact on coupling under bending conditions. The proposed method can be used to analyze various FPCB bending situations.