Multiple Bus Design Methodology for Low Loss and Low Crosstalk with Mesh Ground in FPCB

In this paper, we propose a design methodology for multiple bus structures implemented on flexible printed circuit board (FPCB) with mesh ground structure. The proposed methodology suggested an optimum distance of the signal lines and relative location with respect to the grid to guarantee the $50\Omega$ characteristic impedance without resonance in insertion loss and with minimum crosstalk. Also, the proposed design shows identical impedance of signal lines in time-domain-reflectometer (TDR) measurements and improves Far-End Crosstalk (FEXT) by 4.3 dB in and Near-End Crosstalk (NEXT) 6.1 dB with respect to conventional design (signal lines with $50\Omega$ characteristic impedance at grid center) at 1.25 GHz for the design targeted to be used at C-PHY with 20-mm multiple bus structures in 2-layer FPCB using polyimide.