Multifunctional Space-Time-Modulated Metasurface for Direction of Arrival Estimation and RCS Manipulation in a Single System

In this article, we propose a multifunctional space-time-modulated metasurface (STM-MTS) able to performs simultaneously a direction of arrival (DoA) estimation and radar cross section (RCS) manipulation in a single system. The metasurface consists of an alignment of unit cells, whose scattering response can be dynamically controlled to be transparent(full transmissive unit cell) or opaque (full reflective unit cell),according to the amplitude of the modulating signal applied to the loading p-i-n diodes. The DoA estimation is performed behind the metasurface, i.e., in the transmission region, where multiorder harmonics of the incident field whose complex amplitudes are proportional to the DoA are transmitted. The multiple signal classification (MUSIC) algorithm is employed to estimate DoA. Simultaneously, the monostatic/bistatic RCSs manipulation is performed in front of the metasurface, i.e., in the reflection region, where the reflected field is properly tailored by controlling the modulation scheme at unit-cell level. An X-band STM-MTS is fabricated to experimentally verify the feasibility of the proposed design. A DoA estimation errors are less than 2 degrees inthe incidence angular range of [-50 degrees,+50 degrees] is demonstrated, whereas monostatic and bistatic RCS manipulations of about17 and 36 dB are achieved at operative frequency.