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Body-centric applications include wearable communication systems that can be integrated in many different applications, as for instance in military, security forces, sport, fashion, or medical. In the latter, the quality of life of patients can be greatly improved by the use of implants or wearable systems allowing the continuous monitoring of health related parameters (heart beat, level of glucose, temperature, etc). Ultra-Wideband (UWB) systems have been developed for some of the mentioned applications, and improved antenna designs are needed, especially when the application requires its use in the vicinity of lossy media, such as the human body. This dissertation starts with a thorough review of the state of the art on UWB antennas for selected applications. The theoretical framework for small antennas in the vicinity of lossy media is studied. This is important to understand and characterize the effects of the human body on the antenna behaviour, the radio channel parameters and, hence, the system performance. This thesis focuses on the study of body-worn UWB antennas in the presence of the human body and investigates the effects of their feeding structures and polarization with respect to the body, both in timeand frequency-domain through a combination of full-wave simulations and measurement campaigns. A new simple technique to mitigate the human body effects on the antenna performance is introduced and implemented. An example of an efficient low-profile UWB antenna suitable for wearable applications is proposed. Several experimental investigations are also carried out to study the body proximity influence on the time behaviour of UWB-Wireless Body Area Network (WBAN) antennas in an on-body scenario. An effective approach is also proposed to design band-reject UWB-WBAN antennas by using patch loading, which can be utilized to diminish the interference to the existing wireless communication systems. Finally, this thesis focuses on the diversity gain of UWB diversity antennas. To this aim, two compact printed UWB diversity antennas employing polarization and spatial diversities have been fabricated and the effect on the diversity gain is investigated.