Load impedance measurement on a coaxial cable via time-frequency domain reflectometry

In this paper, a new signal processing based methodology which is able to measure a load impedance with high accuracy and resolution is implemented. This methodology is characterized by a chirp signal with Gaussian envelope which enables one to achieve time localization and to assign energy in the frequency band of interest at the same time. For an evaluating the reflection coefficient and estimating the fault distance on a cable a normalized time-frequency cross-correlation function is utilized, and a cross time-frequency distribution function is used to acquire the phase difference between the input and the reflected signals. The real impedance measurement experiments have been carried out using a time-frequency domain reflectometry (TFDR) system on a coaxial cable with various sorts of terminal resistors. The experimental results of the TFDR based impedance measurement are compared with those of the commercial time domain reflectometry (TDR). The proposed TFDR based impedance measurement methodology shows that it is able to evaluate the location of fault on a coaxial cable and it can offers information of the fault as the load impedance.