RFI Enhancement Technique for FPCB Design Using Trombone Transmission Line Structure

As the available area for mounting components inside mobile devices gets smaller, the radio frequency interference (RFI) between high speed data transmission lines on the flexible printed circuit board (FPCB) and neighboring Wi-Fi antennas increases. This paper proposes trombone line structures on the FPCB used in the camera module to reduce RFI effect on antenna in a smartphone. The trombone structure is proposed to reduce RFI compared to conventional meander lines. E-field, H-field, coupling S-parameter and coupling voltages are obtained using 3D full-wave electromagnetic simulator. The results show the effectiveness of trombone on improving RFI performance compared to conventional structure. All simulation results are obtained using 3D full-wave electromagnetic simulator. Coupling S-parameter is reduced up to 5 dB at resonant frequency of the antenna (@2.4 GHz) in trombone structure. The sensitivity of the receiver antenna is usually less than -100dB, thus the small reduction amount of RFI brings great benefits to the system.