Effect of periodic cable nonuniformities on transmission measurements

Abstract

This paper presents a likely explanation for dips observed in transmission coefficient measurements (S21) for twisted-pair copper cables. We show via computer simulations that periodic cable nonuniformities behave like selective filters, prohibiting electromagnetic wave to propagate at certain frequencies. Similar effect is achieved in optics using fiber Bragg grating (FBG) and may be analyzed as such. The simulation results indicate that periodic cable nonuniformities acting like a FBG is a plausible reasoning to explain the presence of dips.