  In this paper, the channel of an indoor holographic multiple-input
multiple-output (MIMO) system is measured. It is demonstrated through
experiments for the first time that the spatial oversampling of holographic
MIMO systems is able to increase the capacity of a wireless communication
system significantly. However, the antenna efficiency is the most crucial
challenge preventing us from getting the capacity improvement. An extended
EM-compliant channel model is also proposed for holographic MIMO systems, which
is able to take the non-isotropic characteristics of the propagation
environment, the antenna pattern distortion, the antenna efficiency, and the
polarization characteristics into consideration.
