Range Sidelobes Reduction for Pulse-Compression NDT based on Reactance Transformation

Pulse compression is exploited in several measurement procedures where the impulse response of a linear system must be estimated in a noisy environment. In nondestructive testing (NDT), pulse compression based on frequency-modulated chirp signals is applied with sensors of different types. However, the presence of sidelobes in the impulse response retrieved after pulse compression is a major drawback of the method compared to the pulse excitation approach and it degrades the quality of the estimation. To limit this effect, the matched filter is usually shaped by means of windows. In this paper we propose a strategy based on reactance transformation to define a windowing function that outperforms the most used windows in term of near-sidelobes suppression, thus improving the range resolution of the detection system. The paper shows that the proposed filtering technique is particularly suitable for those NDT techniques such as eddy-current and thermography that make use of very broadband excitations. The proposed technique is validated on simulated and experimental test data.