Currently, wireless devices play an important role in everyday life. For ease-of-use, these devices are becoming smaller and require very small antennas. However, the size reduction of these antennas necessarily implies a degradation of their performance. Consequently, the design of electrically small antennas (ESA) requires a very good theoretical understanding of the electromagnetic phenomenon that takes place, especially in terms of accurate performance that can be expected for an ESA with given dimensions. An important parameter of an ESA is its intrinsic quality factor since it is inversely proportional to its impedance bandwidth. Indeed, maximizing the matching bandwidth of an antenna consists in minimizing its quality factor. Facing this problem, many researches have been developed to determine the possible limits of the quality factor of ESA. The first research axis of this thesis is to study the quality factor of ESA to determine whether optimal dimensions exist to approach the fundamental quality factor limits. The second part of the thesis studies miniature antennas for biomedical implants operating at 2.45 GHz. These antennas are printed on a specific microelectronic substrate to ensure a better resolution in terms of metallic traces in order to reduce the size and allow easier integration to facilitate interconnections with RF front-end. The challenge consists in maximizing the performance of these antennas. The presented results are supported by means of electromagnetic models and simulations on one hand. Also, several prototypes are fabricated to validate these simulations.
