This book deals with low-frequency diffraction characteristics of small aperture structures such as a narrow slit and a small hole and their periodic structures, with emphasis on the transmission maximum phenomena through those structures. A narrow slit structure in a conducting plane has been used as a simple model for a narrow slot planar antenna, for example, whereas a small hole structure has been widely used as an aperture-coupling element in a transmission cavity filter or a directional coupler in the microwave regime.
