High frequency signal transfer characteristic of a 40-pin FPC connector

In this paper, we propose an equivalent electrical circuit model of a 40-pin board-to-FPC (flexible printed cable) connector for high frequency signal transfer characteristics. We fabricated an interface board to be fitted in FPC connector (0.5 mm pitch), which enables probing to measure signal transfer characteristics of 40-pin FPC connector. When S-parameters are measured, the unused ports have to be terminated with ideal 50deg resistors, which is not easy for 40 port system. Therefore, we measured signal transfer characteristics of any 2 ports with other 38 ports open, and compared them with the calculated ones from Ansoft HFSS (High Frequency Structure Simulator), which is a commercial software. The coincidence between the measured and calculated ones was excellent up to 3 GHz, which provides the validity of HFSS calculation results. Then the S-parameters are calculated using HFSS software, and equivalent circuit parameters of 40-pin FPC connector are extracted. Finally, S-parameters obtained from the equivalent circuit model showed very good coincidence to the S-parameters from the HFSS simulation.