The MIMO Antenna as a Communication Channel Marco D. Migliore (1) (1) DAEIMI, University of Cassino, Cassino, Italy, http:\\www.unicas.it Introduction The understanding of the connections between information theory and electromagnetic theory is a new topic which is attracting a fast growing number of researchers [1]-[5]. This work represents a further contribution toward the understanding of the connections between these two theories. In particular, in this contribution the antenna is discussed from an usual point of view, in which the antenna itself is treated as a communication channel. This approach allows to understand in a simple way how antennas affect the throughput of a MIMO system. Furthermore, this approach seems to be particularly useful for identifying the intrinsic informational limitations of a MIMO antenna. Ω TX RX Fig 1: MIMO system geometry S x A J M E y F + n O Fig 2: MIMO channel scheme The communication channel approach to MIMO antennas We consider the model of a “pure spatial” communication channel introduced in [2], properly modified to consider a stocastic environment. Since in this communication system information are coded in the spatial variation of the electromagnetic field, instead of temporal variation, this model is particularly suitable to study the behaviour of communication systems in the spatial domain. The input x (Fig 2) represents the primary excitations of the TX antennas. This quantity is the input of the “source distribution” system S, the output of which is the current density J in the space. The current density J is the input of the operator A modelling the radiating process relating J to the field E on a given observation manifold. The measurement system M allows to obtain the measured quantity y. Paper [2] was focused on the identification of the informational limits regarding sources with a given spatial extension, and the operator M (that models the receiving antenna F and (spatially) AWG noise n) was supposed the identity operator plus noise. This work is instead focused on the informational limits regarding the antenna e.g the operator F. In the following we will suppose that F is a linear operator, e.g. the antenna does not include any non-linear devises, like 1901 1-4244-0878-4/07/$20.00 ©2007 IEEE