  The performance and design of the novel single-RF-chain beam-space MIMO
antenna concept is evaluated for the first time in the presence of the user.
First, the variations of different performance parameters are evaluated when
placing a beam-space MIMO antenna in close proximity to the user body in
several typical operating scenarios. In addition to the typical degradation of
conventional antennas in terms of radiation efficiency and impedance matching,
it is observed that the user body corrupts the power balance and the
orthogonality of the beam-space MIMO basis. However, capacity analyses show
that throughput reduction mainly stems from the absorption in user body tissues
rather than from the power imbalance and the correlation of the basis. These
results confirm that the beam-space MIMO concept, so far only demonstrated in
the absence of external perturbation, still performs very well in typical human
body interaction scenarios.
