  In this work, we consider the target detection problem in a sensing
architecture where the radar is aided by a reconfigurable intelligent surface
(RIS), that can be modeled as an array of sub-wavelength small reflective
elements capable of imposing a tunable phase shift to the impinging waves and,
ultimately, of providing the radar with an additional echo of the target. A
theoretical analysis is carried out for closely- and widely-spaced (with
respect to the target) radar and RIS and for different beampattern
configurations, and some examples are provided to show that large gains can be
achieved by the considered detection architecture.
