There has been a continuing pursuit in devloping an ultra-wideband (UWB) time-domain microwave impulse radar nondestructive evaluation (NDE) system at the University of Ilinois at Urbana-Champaign [1]. The UWB time-domain microwave NDE system employs a low power and UWB monocycle pulse sorce [1]. The advantages of the UWB time-domain system are its better spatial resolution, more information of the test targets, and shorter measurement time. However, the time-domain system suffers a worse signal-to-noise ratio (SNR) compared to the fequency-domain system. In order to improve the SNR of the time-domain system, the averaging (stacking), time-gating, and wavelets techniques [8,9] can be applied to the measurement data.
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