The Theory of Uniform Cables - Part I: Calculation of Propagation Parameters

Multipair cables consist of a collection of insulated wires surrounded by other dielectric materials, all of which are usually enclosed in a jacketed, metallic shield for mechanical protection and electrical isolation. T h e wires in a cable are generally helically twisted in pairs and, in practice, other, often undesired, nonuniformities occur along the cable. Nevertheless, the uniform cable, whose wires are straight and parallel, defined by the property t h a t all its longitudinal cross sections are identical, has successfully modeled some aspects of electrical propagation (such as loss per length) over a pair in a cable. 1 Also, some cables are directly modeled as uniform cables; so there is a need for studying uniform cables. Moreover, further experience using the uniform-cable model may lead to a more exact model for nonuniform multipair cables. A rigorous analysis of electromagnetic propagation over uniform cables, starting from Maxwell's equations, was p e r f o r m e d by Carson 2 for cables having homogeneous dielectric material separating the wires. 597