Joint Time-Frequency Domain Reflectometry for Diagnostics of Coaxial Cables

The importance of aging electrical wiring and associated faults in aircraft has been highlighted due to the critical effects on the safety of overall systems. Traditional reflectometry methods for the detection and localization of the faults on cable have been achieved in either the time domain or frequency domain only. In this paper, we introduce a new high-performance reflectometry technique that operates simultaneously in both the time and frequency domains. The joint time-frequency domain reflectometry (JTFDR) utilizes time and frequency information of a transient signal to detect and locate the fault. The approach rests upon time-frequency signal analysis and utilizes a chirp signal multiplied by a Gaussian time envelope. The Gaussian envelope provides time localization, while the chirp allows one to excite the system under test with a swept sinusoid covering a frequency band of interest. Sensitivity in detection and accuracy in localization of the reflected signal are provided by a time-frequency cross correlation function. The proposed approach is verified by experimentally locating various types of faults, located at various distances, in coaxial cables in comparison with classical time domain reflectometry (TDR). Knowledge of time and frequency localized information for the reference and reflected signal gained via time-frequency analysis, enables an automated detection and accurate localization of the faults on cables.