Spatial Diversity in Radar Detection via Active Reconfigurable Intelligent Surfaces

Active reconfigurable intelligent surfaces (RISs) are a novel and promising technology that allows to control the radio propagation environment, while compensating for the product path loss along the RIS-assisted path. In this letter, we consider the classical radar detection problem and propose to use an active RIS to obtain a second independent look of a prospective target illuminated by the radar transmitter. At the design stage, we select the power emitted by the radar, the number of RIS elements, and their amplification factor in order to maximize the detection probability, for a fixed probability of false alarm and a common (among radar and RIS) power budget. An illustrative example is provided to assess the achievable detection performance, also in comparison with that of a radar operating alone or with the help of a passive RIS.