Diffraction control for electrically small low-profile antennas

Electrically small antennas (ESA) place additional limitations on the antenna designer. These limitations are: low efficiency, narrow bandwidth and a strong dependence on the mounting structure.; A review of these limitations is performed and allows us to redefine the design parameters, such as the Gain-Bandwidth (GBW), when dealing with the ESA. The GBW product of an antenna is a powerful tool when determining the capabilities of an antenna since it is independent of the feeding structure and the matching network.; The independence of the antenna properties with the mounting structure is accentuated in ESAs due to the strong reactive near fields around the antenna. The diffraction of near fields has to be studied in order to understand the relation between an ESA and its mounting structure. The idea of controlling the manner in which waves diffract off finite structures is exemplified by the use of Artificial Magnetic Conductors (AMC) as surface wave inhibitors; therefore the diffraction off AMC edges is studied. AMCs were proven to decouple two antennas placed together due to the AMC's surface wave suppression property. However, when designing the ESA the practical implementation of an AMC at low frequencies might be prohibitive due to space limitations.; In this dissertation an inclusive study of the attempts to mimic the properties of AMCs within a minimized surface is presented. The various dispersive materials can be categorized as metamaterials, since they exhibit properties not found in nature at certain frequencies. These metamaterials are found to control diffraction; however, they might or might no be suitable for a specific design depending on the antenna implementation.