Effects of Braid Resistance and Weatherproofing Jackets on Coaxial Cable Shielding.

摘要

The effects of finite conductivity in the shield conductors and of the presence of dielectric weatherproofing jackets on coaxial cable shielding are investigated by considering three coaxial-cable shield models. The first of these is a bidirectionally conducting shell; the second is a concentric pair of counter-wound filamentary helices with a (possibly lossy) dielectric jacket. For each model, the transmission-line parameters are determined. Comparison of the results for the first two models indicate the importance of the woven shield structure, in that for the first model, the coupling impedance decreases exponentially as the shield thickness increases; and for the second, the decrease is generally only algebraic. The results for the third model indicate that a dielectric jacket tends to reduce the electric-field coupling to the interior of the cable, and that the finite resistance of the shield conductors for this case is not of great importance as long as it is small.