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A programmable metasurface antenna based on electrically tunable elements operating in 5G millimeter‐wave band, which has the features of low cost, easy manufacturing, low profile, easy integration with planar circuits, is proposed herein. The prototype consists of a 128‐element metasurface array, an 8‐channel beamforming chip as equal amplitude power divider networks, and a control network. Elements mounted with varactors to realize different states are controlled by DC bias signal from the back of a printed circuit board (PCB). By assigning different voltage values, array coding can be dynamically changed, thereby realizing beam steering. Both element dimensions and its location along substrate integrated waveguide (SIW) are optimized to better antenna performance. Experiment results show that the proposed metasurface can achieve not only the scanning range of ±70° for unidirectional beam in azimuth and ±40° in elevation but also ±50° for dual beam in azimuth. The whole prototype is fabricated based on PCB technologies, and good agreements among simulated and measured results are obtained. The proposed electrically tunable metasurface array is a good alternative to the traditional expensive phased array and has a great potential application prospect in radar and communication systems. [ABSTRACT FROM AUTHOR]

The photonic spin Hall effect (SHE) arises from the spin–orbit interaction of lights and plays an important role in light–matter interactions. The phenomenon of spin‐momentum locking validates photonic SHE with unprecedented abilities in wave manipulation. Here, the directional coupling and spin‐momentum locking in spoof surface plasmon polaritons (SSPP) are demonstrated. The transverse spin angular momentum in SSPP is calculated using effective medium theory and the study shows the spin direction is inherently locked to the propagation direction, thus manifesting the spin–orbit interaction of electromagnetic (EM) waves. The spin‐momentum locking is further verified by projecting linearly and circularly polarized waves onto a scatterer‐SSPP structure. It is observed that the helicity of the incident EM wave governs the propagation direction of excited SSPP modes and the directional coupling originates from constructive and destructive interferences of two orthogonal modes. Reconfigurable transmissions of SSPPs are further demonstrated. The proposed design can find applications in reconfigurable sensors, antennas, and power dividers. This approach demonstrates the spin‐momentum locking in SSPPs and introduces new degrees of freedom to manipulate SSPPs by engineering the helicity and interference of EM waves. [ABSTRACT FROM AUTHOR]

Direction-of-arrival (DOA) estimation is one of the most critical technologies of radar, remote sensing, and wireless communications. The traditional DOA estimation is closely related to phased array antennas, which require complicated and expensive hardware and high-power consumption. Metasurface can manipulate electromagnetic waves without using massive transceivers, which makes it possible to realize antenna arrays in a cost-effective way. Here, we propose a strategy of DOA estimations by using a time-domain-coding digital metasurface and a single receiver. Specifically, the incident wave on the metasurface is modulated by the time-domain orthogonal codes impressed on the meta-atoms, and their amplitude and phase distributions are precisely retrieved from the signals detected by the receiver antenna. The effectiveness and accuracy of the proposed strategy are verified by experiments on a two-dimensional metasurface with individually addressable meta-atoms. The strategy features low cost and high flexibility and will facilitate various wireless applications. [ABSTRACT FROM AUTHOR]

Digital coding metasurfaces have attracted considerable interest, owing to their ability to manipulate electromagnetic waves and implement various functionalities with programmable controls. These metasurfaces offer high‐resolution and high‐speed responses; thus, they are implemented in high‐speed imaging, nondestructive sensing, and wireless communication. However, traditional active metasurfaces are typically based on semiconductor components, which are difficult to realize at terahertz frequencies. Additionally, non‐magnetic transmissive metasurfaces cannot realize a large phase‐tuning range without increasing the number of metasurface layers. Herein, a 1‐bit transmissive digital coding metasurface based on liquid crystals is proposed to achieve programmable terahertz beam manipulations with electric control. The Fano resonance that is excited in the asymmetrical metasurface element enables a larger phase variation while maintaining the transmittance. The proposed digital metasurface can effectively achieve many functionalities, such as dual beam steering, multiple beams, and orbital angular momentum beams, via altered coding patterns; an example of dual beam steering is experimentally verified. This study is expected to provide a promising method to manipulate transmissive terahertz beams using a digitally programmable metasurface, and it has potential applications in imaging, sensing, and wireless communications. [ABSTRACT FROM AUTHOR]