Analysis of the helical twisted-wire pair running above ground: transfer function evaluation

This paper deals with the analysis of an internally excited three-conductor nonuniform transmission-line system comprising a twisted wire pair (TWP) running above a conducting plane. Research is conducted aimed at the analysis and characterization of the propagation properties of a helical-type TWP system with lossy conductors. Numerical simulation results regarding the attenuation and phase-velocity characteristics of this transmission-line system are obtained by using a TWP model consisting of a cascade of small incremental parallel segments subjected to continuous rotation. Special attention is paid to the derivation and analysis of the frequency-domain voltage transfer function describing the behavior of the TWP structure with a number N of twists. Time-domain results concerning the system response to a pulse train excitation are also obtained by making use of the information conveyed by the transfer function. Both frequency- and time-domain simulation results reported here show that the periodicity arising from wire twisting may dramatically modify the transmission-line system propagation properties as compared to those concerning the untwisted case.