Characterization of transmission lines based on frequency-domain and time-domain measurement techniques

Abstract

The importance of electrical cables in modern data communication and power transmission systems cannot be overstated. Efficient and secure transmission of either data or energy depends on the healthy state of electrical cables and cable networks. In many applications, the continuous monitoring of cable characteristics is required in order to guarantee system performance. In this work, different time-domain and frequency domain techniques are applied to a set of experiments to explore different means to characterize transmission lines in a comparative manner. First, two exemplary cables are analyzed by frequency domain techniques to obtain their capacities in function of different cable lengths. Results show the influence of length over channel capacity for both cables, which were compared to commercial data transmission systems. As a second part of the experiments, a chosen cascaded transmission line set is characterized in time and frequency domain. Time domain analysis based on reflectometry and transmissometry methods reveals impedance mismatches along the line and impulse response respectively. Frequency domain analysis is based on the scattering parameters and enables the extraction of the electrical parameters of the channel. Also, time domain analysis of scattering parameters can be performed by the inverse chirp Z transform, a weak approach generally based on a minimum norm solution. Since the nature of the impedance mismatches along the line is sparse, it is proposed a sparse inverse chirp Z transform, specially designed for this kind of application. The method is verified by comparing results provided by the general approach, showing promising performance through the reflection and transmission profiles obtained.