Reconfigurable antennas for adaptive MIMO communication systems

Daniele Piazza

doi:10.17918/etd-3037

The requirements for the next generation wireless systems seek to provide reliable high data rate at low cost. Unfortunately the current wireless communication infrastructure is not fully equipped to cover this unprecedented quality of service. Major obstacles include: limited bandwidth availability, limited transmit power, and signal strength uctuations which are intrinsic to the multivariate wireless channel. Multiple Input Multiple Output (MIMO) antenna systems have emerged as one of the most significant technical breakthrough in modern wireless communications able to satisfy these stringent requirements. However the necessity of assuring a high data rate in a large variety of environments while reducing the antenna array space occupation on portable devices requires an improvement in current MIMO technology. To overcome these limitations, we propose in this thesis, the use of reconfigurable antennas that adaptively change, through RF switches, their radiation properties and frequency of operation according to wireless channel characteristics. The key idea of this work is to show that reconfigurable antennas, through their capability to dynamically change their electrical and radiation properties, can be used to change the propagation characteristics of the wireless channel existing between the transmitting and receiving antennas. The proposed MIMO system breaks from the conventional wisdom that the wireless propagation channel cannot be changed intentionally by the transceivers in the link. Three different novel classes of electrically multi element reconfigurable antennas are proposed as suitable candidates for reconfigurable MIMO systems: i ) a reconfigurable printed dipole antenna array that exploits inter element mutual coupling to achieve pattern reconfigurability, ii ) circular patches capable of exciting higher order modes to achieve pattern and polarization diversity, and iii ) a metamaterial leaky wave array that can be reconfigured in pattern to achieve unprecedented degrees of pattern reconfigurability. To effectively use such antennas with actual communication systems, a low power consumption method for selecting the array configuration is proposed. This technique exploits the close relationship between the environment that surrounds the antenna array and the antenna radiation characteristics in order to select optimal array radiation patterns without the need for intense channel sensing or excessive training. A complete reconfigurable antenna system composed of mutli-element reconfigurable antennas and a control unit capable of efficiently driving the antennas is proposed to deliver unprecedented system performance. Analytical models of the proposed system are used to fully characterize the functionality and performance of the technology. A complete evaluation of the proposed system is conducted through electromagnetic simulations and field measurements collected with a channel sounder specifically designed to measure the performance of multi element antenna systems. It is demonstrated that the novel multi element reconfigurable antenna system is capable of providing i ) increased data rate compared to common non reconfigurable antennas in single link communications as well as in multi-link ad hoc networks, ii ) reduced space occupation by the antenna on the communication device exploiting the principles of pattern and polarization diversity, iii ) reduced number of radio-frequency chains needed at the receiver/transmitter and iv ) reduced amount of transmit power for achieving performance comparable to that of standard non reconfigurable antenna systems.

Reconfigurable antennas for adaptive MIMO communication systems

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Reconfigurable antennas for adaptive MIMO communication systems

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