Backscattering in Twisted-Pair Nonhomogeneous Transmission Lines

Abstract

The development of the communication networks tends gradually toward exploiting higher frequencies, sometimes even reaching the lowest microwave band (P-band). As the signal bandwidth used for transmission over twisted-pairs increases, as recommended by G.fast and other broadband systems, new phenomenon was observed, namely, backscattering. Motivated by the measurements of copper cables in frequency band up to 400 MHz, we propose a novel backscattering model. It may be productively applied to the problem of loop diagnostics. The methods to accurately and reliable determine the relevant transmission-line parameters are sine qua non condition to appropriately exploit the potential of short-to-medium range access lines. In this paper, a recursive formulation of the frequency-domain response of the backscattering is used for a space–time characterization. To confirm the practical use of the finding, we evaluate the properties of a loop using wideband, high-frequency $S_{11}$ measurements of the real cables. These laboratory results confirm the effectiveness and accuracy of the proposed method.