Near-field microwave imaging utilizing tapered rectangular waveguides

Open-ended rectangular waveguides have been used conventionally as imaging probes in the measurement systems developed for near-field microwave nondestructive evaluation (NDE) purposes. These systems have attained an increasing interest as they have proved to be competent in wide spectrum of applications - i.e. imaging of subsurface inclusions in composite structures. The lateral resolution of these probes, and hence the quality of the captured images, is inversely proportional to the electrical area of the waveguide aperture. In order to obtain images of high fidelity for small sized concealed entities, the resolution of the rectangular waveguide probes should be enhanced. In this paper, it will be shown that smoothly tapering the waveguide´s aperture in the E-plane significantly improves the spatial resolution of the imaging system. The potential of the proposed probe on the quality of captured images will be demonstrated in real-life NDE problem. Furthermore, the resolution of the new probe will be compared to that of the conventional one.