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The fast growth of wireless communications has driven the necessity of exploiting technological solutions for the needs of faster connectivity. While bandwidth allocation and effective radiated power (ERP) are subjected to regulatory constrain, alternative solutions have been developed to overcome the challenges that arise in terms of wireless coverage and number of users. Reconfigurable antennas (RAs) technology is one of the hardware solutions developed to enhance the connectivity between wireless devices. These new class of radiating elements are able to adapt their physical characteristics in response to the environmental changes or users density and location. Reconfigurable antennas can be divided into two main categories: frequency reconfigurable antennas and pattern reconfigurable antennas. The former class of RAs are able to switch the operational frequency in order to move the communication within unoccupied channels. The latter category defines those antennas that are able to change their radiation characteristics (radiation pattern or polarization) in response to the dynamics of the surrounding environment. Unlike conventional static antennas where the energy is wasted around the surrounding space, the use of RAs allows for a smarter management of the radiated energy as the beam can be focused toward specific directions. As a result, not only data throughput between two devices can be improved but also the interference between adjacent networks can be reduced significantly. In this PhD thesis we focus on the design, prototyping and system application of compact RAs for wireless base stations and mobile devices. Specifically, the first task focuses on the design of a compact reconfigurable antenna capable of generating omnidirectional and directional beams in a single planar design. Next, we propose to apply a miniaturization technique in order to drastically reduce the size of Composite Right-Left Handed Reconfigurable Leaky Wave Antennas (CRLH RLWAs). The large beam steering capabilities along with the miniaturized dimension open new venues for the integration of this antenna technology into mobile devices such as laptop or tablets.  Similarly for electrically reconfigurable antennas, characteristics such as input impedance and radiation properties of a radiating element can vary by mechanically change its physical dimension. In other words, instead of changing the metallic geometry through electrical components, the characteristics of an antenna can be changed through physical deformation of its geometry. This principle addresses the second main application of reconfigurable antennas this PhD thesis.

Wearable technologies are gaining a lot of attentions due to their strong potential for sensing, communication and tactile interaction applications. Thanks to the progress in knitting facilities and techniques, smart fabrics are generally implemented through sewn-in sensors especially in the fields of medical and athletic applications. Such wearable sensors provide a means to monitor the wearers health through physiological measurements in a natural setting or can be used to detect or alert care providers to potential hazards around the wearer. The feasibility of building electrical devices using conductive fabrics has been analyzed through electrical characterization of textile transmission lines and antennas where conductive fabrics have been applied onto woven fabrics have been demonstrated in recent literature. Previous works show conductive copper foils or fabrics bonded to a flexible substrate. However, these techniques show limitations in terms of electrical losses caused by adhesives or glue chemicals. It is desirable to address these drawbacks by knitting conductive and non-conductive yarns in a single process resulting in smart textiles that are unobtrusively integrated into the host garment so as to eliminate the need for chemical adhesives that degrade electrical performance. The characteristics variations of a fabric-based antenna under physical deformations can be exploited to provide a fully wireless sensing of certain body movements. The second task of this PhD thesis, focuses on the design and testing of these purely textile wireless sensors for biomedical applications. The Radio-Frequency Identification (RFID) technology will be applied fordesigning fabric-based strain sensors through the use of novel inductively-coupled RFID microchips (MAGICSTRAP). As opposed to conventional surface-mount microchips, the MAGICSTRAP does not require any physical soldering connection as the RF energy is inductively coupled from the microchip pads to the antenna arms. A separate interrogator unit can communicate with this knit passive RFID architecture by sending a probing signal; the backscattered component received from the knit tag will indicate the level of stretch, and this information will be translated in the physical phenomenon being monitored. The change in the electrical characteristics of the textile antenna, along with the decoupling of the MAGICTRAP chip allow for more reliable detection of contraction/elongation movements. This study will include comprehensive design and characterization of the textile tag sensor along with performance analysis using a mechanical human mannequin.