  In this paper, we put forth the idea of metaprism, a passive and
non-reconfigurable metasurface acting as a metamirror with frequency-dependent
reflecting properties within the signal bandwidth. We show that, with an
appropriate design of the metaprism, it is possible to control that each data
stream in an orthogonal frequency division multiplexing (OFDM) system is
reflected in the desired direction without the need for control channels and
channel state information (CSI) estimation between the base station and the
metaprism, but simply by correctly assigning subcarriers to users. Furthermore,
the metaprism can also be designed so that it focuses the signal towards a
specific position depending on the subcarrier, provided that it is in the
near-field, with consequent path-loss reduction. A critical discussion is also
presented about the path-loss gain obtainable from metaprisms and, more
generally, from metasurfaces. The numerical results show that this solution is
surprisingly effective in extending the coverage in areas experiencing severe
non line-of-sight (NLOS) channel conditions, thus making it a very appealing
alternative to reconfigurable metasurfaces when low-cost, no energy
consumption, and backward compatibility with existing wireless standards are
required.
