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An innovative method utilizing microwave nondestructive testing and evaluation (NDT&E) techniques for enhanced detection and evaluation of rust under paint has been developed. The results are promising, and they show that the use of a layer of dielectric material with known properties to replace the standoff layer (air) yields significant improvements in the measurement sensitivity and resolution for some microwave NDT applications. The goals of this investigation were pursued and achieved using theoretical electromagnetic computer programs describing the interaction of microwave signals radiated out of an open-ended rectangular waveguide with any layered medium. One of the computer programs calculates the aperture reflection coefficient (simulating measurements), and the other computer program calculates the field distribution in any layered media. The experimental results were obtained using an inspection system that was built according to the results of the theoretical investigation, and they confirmed the theoretical results.