Wireless networks consisting of compact antennas find applications in diverse areas such as communication systems, direction of arrival estimation, sensor networks and imaging. The effectiveness of many of these systems depends on maximizing the reception of RF power and extracting maximum information from the incident electromagnetic wave. Traditionally, this has been achieved through MIMO systems employing a spatial array of antennas, and results in enhanced channel capacity. We show that similar increases in capacity can be obtained through the use of vector antennas consisting of co-located loops and dipoles that can respond to more than one component of the incident electromagnetic field. Such a system is constructed and its performance measured in a rich scattering environment. It is shown that the system, with three and four element vector antennas at both the transmitter and receiver, supports three and four times more information, respectively, as compared to conventional systems consisting of sensors with single antennas. Alternate geometries evolving out of the study of co-located antennas, consisting of closely spaced elements with optimized mutual coupling and envelope correlation characteristics are discussed. The design and implementation of filter networks that act as conjugate matching networks and enable better absorption efficiency is described. The enhancement in the Expected Mutual Information of systems employing such filters in conjunction with vector antennas is quantified for the designed antennas. Preliminary results indicating possible applications of vector antennas to medical imaging are also included.
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