Implementation and characterization of a reconfigurable time domain reflectometry system

Abstract

A practical architecture for pulsed radar and time domain reflectometry (TDR) is presented in this paper. Incorporating the software-defined radio paradigm, the prototype features a reconfigurable transceiver. Reconfigurability is achieved by implementing an arbitrary waveform generator (AWG) in a Field Programmable Gate Array (FPGA) and suitable digital-to-analog converters (DAC). The AWG allows for changes in the width and shape of a transmitted pulse on-the-fly, i.e. without the need for reprogramming. In the current implementation, the transmitter is able to achieve a minimum pulse width of 6.25ns, which result in a 62.5 cm range resolution for non-dispersive medium with 0.67 velocity factor. The resolution was verified by testing several cable setups with two differently-spaced discontinuities. The receiver, on the other hand, employs equivalent time sampling (ETS) through on-board analog-to-digital converters (ADC) and a custom delay generator. The ETS receiver was able to attain 0.357ns equivalent time sampling interval, which is equivalent to a 2.8 GHz sampling rate for periodic signals. This allows the transceiver to locate a discontinuity with 3.57cm accuracy in a non-dispersive medium with a velocity factor of 0.67, which was verified through experiments performed on open circuit-terminated cables with varying length. The system is intended to be used in detecting faults on a TDR cable buried underground to detect slope movement.