Fast Chirp Frequency-Modulated Continuous-Wave Reflectometer for Monitoring Fast Varying Discontinuities on Transmission Lines

A portable fast chirp frequency-modulated continuous-wave (FMCW) reflectometer is presented to locate and monitor fast varying discontinuities or faults on transmission lines. This frequency-domain reflectometry (FDR) approach exploits and adapts the advantages of the closely related and frequently employed FMCW radar principle to transmission line reflectometry and overcomes the limitations of commonly used time-domain reflectometry (TDR) methods. The signal generation is based on direct digital synthesis (DDS) and frequency multiplication in order to exploit the advantages of DDS technology, e.g., fast and agile sweep time, and to overcome the drawbacks of analog signal sources related to nonlinearities, temperature sensitivity, or phase noise. By this means, the presented reflectometer provides highly linear, broadband, and fast swept chirp pulses with a duration on the order of microseconds with an initial frequency in the lower UHF-band and a bandwidth of 5.2 GHz. The system concept, its hardware realization, and performance specifications are introduced. The first laboratory test results for static transmission lines and a dynamic measurement setup are presented. The results demonstrate the effectiveness, versatility, and fine ranging capabilities on the order of 2 cm of this approach.