  Originally introduced in the early 2010's, the idea of smart environments
through reconfigurable intelligent surfaces (RIS) controlling the reflections
of the electromagnetic waves has attracted much attention in recent years in
preparation for the future 6G. Since reconfigurable intelligent surfaces are
not based on increasing the number of sources, they could indeed pave the way
to greener and potentially limitless wireless communications. In this paper, we
design, model and demonstrate experimentally a millimeter wave reconfigurable
intelligent surface based on an electronically tunable metasurface with binary
phase modulation. We first study numerically the unit cell of the metasurface,
based on a PIN diode, and obtain a good phase shift and return loss for both
polarizations, over a wide frequency range around 28.5 GHz. We then fabricate
and characterize the unit cell and verify its properties, before fabricating
the whole 10 cm x10 cm reconfigurable intelligent surface. We propose an
analytical description of the use that can be done of the binary phase RIS,
both in the near field (reflectarray configuration) and in the far field
(access point extender). We finally verify experimentally that the designed RIS
works as expected, performing laboratory experiments of millimeter wave
beamforming both in the near field and far field configuration. Our
experimental results demonstrate the high efficiency of our binary phase RIS to
control millimeter waves in any kind of scenario and this at the sole cost of
the energy dissipated by the PIN diodes used in our design.
