Compact Multiple Antennas in a Random World

Recent work on compact multiple antennas in a random environment is reviewed, including extensions of the energy density antenna and the MIMO cube. The performance of handsets with multiple antennas is dependent on many factors due to the close proximity of the antennas. The distribution of scatterers in the environment has an impact on the distributed directivity of the antennas, the powers absorbed in the loads, and the correlation between the open-circuit signals. Matching the antennas is non-trivial, since the matching changes the output correlations and the efficiency. The antennas may be matched for maximum MIMO capacity for a given environment. Basic bandwidth limitations are also discussed.