Study on grounding condition of shield sheath in shielded twisted pair cable

Recently, the application field of a high-speed differential transmission system has expanded, and shielded twisted pair cables (STP cables) are used for the system. Therefore, it is necessary to understand the characteristics of the STP cable. In this paper, we study the relation between noise susceptibility performance of a STP cable and terminal grounding condition of the shield sheath of the STP cable. We have evaluated noise induction level of STP cables with various terminal grounding conditions of shield sheath using mixed mode S-parameter measurements. As a result, it is found that pigtail ground connection of the sheath is not enough to obtain low noise susceptibility performance. It is also found that the performance can be improved by using plural pigtails which connect the shield sheath circumference symmetrically to the ground.