Spatial Diversity in Radar Detection via Active Reconfigurable Intelligent Surfaces

Active reconfigurable intelligent surfaces (RISs) are a novel and promising technology that allows controlling 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 get a second independent look at 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.

Reconfigurable intelligent surfaces (RISs) allow controlling the radio propagation environment, thus providing novel degrees of freedom for the design of wireless systems [1], [2]. An RIS is a low-cost passive flat surface made of sub-wavelength refractive/reflective elements (atoms) that can add a tunable phase shift to the incident electromagnetic wave. The atoms are controlled using an embedded logic with a power consumption that is usually negligible and, all together, can redirect the planar or spherical wavefront hitting the surface in several ways. E.g., a diffuse scattering, an anomalous reflection, or a beam focused towards a specific point can be produced; in addition, a data message can be even superimposed on the redirected signal [3], [4]. RISs have been used to boost the performance of wireless communication links [5]–[7]; they have been also proven effective in other contexts, including wireless power transfer [8], localization and mapping [9], [10], joint communication and sensing [11], and, more recently, target detection [12]–[14].