Experimental Analysis and Modelling of Coaxial Transmission Lines with Soft Shield Defects

Abstract : Significant research has focused on the diagnosis of “hard” faults (open and short circuits) in transmission lines, but there has been much less work on “soft” faults resulting from a very small change in line impedance. This research is based on one type of soft fault problems in electrical fault diagnosis; the impacts of partial degradation in the coaxial cable shielding or other shielded lines. At first, using classical transmission-line equations in the frequency domain, analytical expressions are derived to infer the impact of the very small discontinuities in transmission lines. Then, this paper illustrates the real experimental measurement cases of faulty shields on coaxial cable. The experimental studies of fault length effects are presented in frequency and time domain measurements by referring to a coaxial cable transmission line designed for high frequency signal transmission in aircraft radio communication systems. Finally, numerical simulation of the experimental case is presented and then validated against the measurement result by using a data processing technique based on time domain analysis.