On Electromagnetics and Information Theory

Some connections are described between electromagnetic theory and information theory, identifying some unavoidable limitations imposed by the laws of electromagnetism to communication systems. Starting from this result, the role of the degrees of freedom of the field in radiating systems is investigated. Different classes of antennas use the available degrees of freedom in different ways. In particular, a multiple-input multiple-output antenna is a radiating system conveying statistically independent information on more than one degree of freedom of the field. Applications of the theory to antenna synthesis and antenna characterization in complex environments are shown.