Accurate Characterization of Electromagnetic Coupling Through Hollow Shields With TWP Cables Over an Ultrawide Frequency Range

The electromagnetic coupling through a hollow shield of a shielded twisted-wire pair (TWP) cable is thoroughly characterized in this paper. Initially, the transfer impedances of the hollow shield are generalized to account for both the skin and proximity effects, considering the irregular distribution of the current on the inner and outer surfaces of the shield. Subsequently, the common-mode (CM) and differential-mode (DM) transfer impedances of the shielded TWP are formulated over a wide frequency range. The analysis reveals that the DM transfer impedance cannot be neglected due to the considerable influence of the proximity effect on the shield surfaces. Moreover, the induced CM and DM currents in a shielded TWP situated near an additional shield are accurately predicted using transmission line theory combined with the developed modal transfer impedances. Building on this, the proposed theory is extended to encompass multishielded structures by employing recursive formulas that account for the influence of all nearby shields. The accuracy of the proposed formulas is validated by comparing the results with those generated by HFSS software, demonstrating strong agreement across various scenarios.