Terminal Response of Braided-Shield Cables to External Monochromatic Electromagnetic Fields

This paper has two purposes: (1) to assess the relative importance of magnetic and electric coupling parameters of braided shields in the determination of terminal response of braided-shield cables to external electromagnetic fields and (2) to compare a postulated coupling model with those on which various experimental determinations of shielding effectiveness have been based. In the first case, formulas for certain special conditions of wave incidence and sheath-conductor terminations are obtained, but their implications are not explored in detail. In the second case, certain discrepancies among various published methods of measurement and between the measurements and the postulated model are noted. The paper also shows formally how the external-field coupling parameters to each conductor of a multiconductor cable may be determined. A review of earlier work indicated that measurements made in the past have been largely incomplete. In some cases, only the effect of the inductance parameter was measured; in others, the composite effect of both inductive and capacitive coupling was measured, but attributed to inductance only. In either category, this analysis shows that the use of such a limited physical model will generally lead to inaccurate predictions of cable terminal response.