Accurate 2-D DoA Estimation Based on Active Metasurface With Nonuniformly Periodic Time Modulation

A novel direction of arrival (DoA) estimation method based on amplifier-integrated active metasurface is proposed to find multisource directions by a single-channel system. Nonuniformly periodic time modulation (NPTM) on the metasurface reduces the hardware complexity by taking full advantage of the spectral resources. As a result, only partial metasurface elements are required to achieve 2-D DoA estimation, while the remaining elements can be redesigned and encoded to control electromagnetic waves. Thus, adaptive beamsteering can be expected to realize in a full-duplex way. Moreover, the amplifiers in the metasurface can function as modulation units to generate the required harmonics and enhance signal quality. The nonideality of the modulated square wave due to the active devices is allowed without affecting the estimation accuracy. An active metasurface prototype composed of 5 $\times $ 5 elements is fabricated and measured in the microwave anechoic chamber for multisource direction finding. The measured maximum error is 0.31°, which is high accuracy compared with the state-of-the-art works. Thus, the proposed method has application values in the Internet of Things (IoT), wireless communications, and radar.