Microwaves incident on finite dielectric structures, such as slabs and hollow wedges, excite a variety of fields that produce complicated interference patterns. This paper describes calculations with the moment method and measurements with a small, probe antenna. The interpretation identifies guided waves, plane waves, and cylindrical waves, and it gives relative amplitudes of these waves. The intensity distribution is a hologram because the guided waves and internal refracted waves are coherent but with distinct propagation constants. Images are formed by reconstruction. In addition, describe a new, angle scanning interferometer that determines angular distributions of fields about dielectric gratings. Mechanismus, which include grating lobes, and specular reflections, are identified.