Direction Finding by Space–Time-Modulated Digital Metasurface With Harmonics’ Amplitude Correlation

The application of digital metasurface (DM) in direction finding (DF) has been widely studied. However, numerous nonideal properties of practical DM are difficult to be modeled and decrease the DF accuracy. Consequently, a simple but effective DF method based on space–time-modulated DM is proposed in this article. The fundamental principle is described as follows. Signals that are transmitted or scattered by practical space–time-modulated DM will generate numerous harmonics. There is a unique mapping between the relative amplitudes of these harmonics and the incident angle of the source. Consequently, a database of the harmonics’ amplitude and their corresponding incident angles is pre-established. Subsequently, the signal to be measured is incident on the space–time-modulated DM, and the generated harmonics are collected. By performing a correlation operation with the harmonics’ amplitude in the database, the incident angle is ultimately estimated. Since the database is built based on practical DM, the method has taken into account the nonideal properties of DM, thereby not only enabling straightforward and highly accurate 2-D angle estimation but also reducing the requirements for DM design and increasing practicality. Ample numerical simulations have corroborated the effectiveness of the proposed method. Moreover, an S-band reflective 1-bit DM has been fabricated, and a 1-D angle estimation outcome has been achieved experimentally. Over the range from 10° to 170°, it exhibits a maximum absolute error (MAE) of 0.8° and a root-mean-square error (RMSE) of 0.18°. It is believed that this method will find applications in the fields of the Internet of Things (IoT), communication sensing integration, and other related areas.