In the last years, Multiple Input Multiple Output (MIMO) systems have become the cornerstone of the future of Wireless communications. The performance of these systems in terms of channel capacity has meant that transmission rates that were impossible some years ago can be real nowadays. Unfortunately, MIMO systems have a characteristic that can mean a problem in the Wireless and mobile market, in where the eagerness to minimize the size of the devices is one of the mainly objectives. This non-desirable characteristic is the difficulty when compacting multiple active antennas (and, hence, their corresponding radiofrequency chains) in a handset terminal. Therefore, the idea of finding other alternatives that could emulate the behaviour of having multiple antennas represents a quite attractive and wide research area. The use of parasitic elements seems to be the most effective alternative when designing compact antennas for MIMO systems. In fact, the inclusion of these elements around an active antenna allows us to orient the beam towards different directions, what can be a quite interesting approach to have multiple antennas. Therefore, the idea is simple: just having one active element and a set of parasitics surrounding it, we can orient the beam towards different directions in order to maximize the channel capacity with a small impact on the features and with clear advantages in terms of compacting and cost. In this sense, parasitic elements can be used in order to implement different kinds of antennas. Two of the most common are Adaptive Antennas and rotating Switched Parasitic Antennas. In this thesis, we will explore both possibilities, and two different antenna technologies will be researched: monopoles antennas and patch antennas. A complete study of both of them will be carried out and the research will be oriented to two mainly aspects: antenna performance and achieved channel capacity.Ingeniería de Telecomunicació
