Effects of target resonances on ultrawideband-DORT

Abstract

In this paper, we investigate the effects of target (scatterer) resonances on the decomposition of the time reversal operator (DORT) applied to ultrawideband (UWB) electromagnetic scattering. When UWB-DORT is applied to well-resolved point-like scatterers, the frequency responses of the scatterers remain mostly identical and the detected targets appear as a set of distinct eigenvalues over the entire frequency band of operation. However, this may not be the case for targets with strong resonances, since the strongest eigenvalue may not correspond to the same scatterer at different frequency points depending on the resonance characteristics of each target, rendering the eigenstructure inconsistent over the band. Such an effect limits the ability to characterize the targets and construct UWB signals for selective focusing. We examine this phenomenon via numerical experiment considering various target configurations. We also demonstrate a method to overcome this eigenstructure mixing' by simply correlating adjacent frequency points when applying UWB-DORT. A robust UWB-DORT process applicable to various types of targets would enhance the capability of DORT as a method of target characterization/identification in addition to selective focusing.