  In order to support multiple antennas on compact wireless devices,
transceivers are often designed with matching networks that compensate for
mutual coupling. Some works have suggested that when optimal matching is
applied to such a system, performance at the center frequency can be improved
at the expense of an apparent reduction in the system bandwidth. This paper
addresses the question of how coupling impacts bandwidth in the context of
circular arrays. It will be shown that mutual coupling creates eigen-modes
(virtual antennas) with diverse frequency responses, using the standard
matching techniques. We shall also demonstrate how common communications
techniques such as Diversity-OFDM would need to be optimized in order to
compensate for these effects.
