The understanding of the connections between information theory and electromagnetic theory is a new topic which is attracting a fast growing number of researchers. 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.