The rapid development of metasurfaces offers new possibilities to establish novel wireless communication systems with simplified architectures. However, the current demonstration systems are based on the reflection-type metasurfaces, which suffer from high profiles and integration challenges in practice. Such configurations are also inefficient for handling multiple subcarriers during beam scanning and beam tracking. To address these limitations, a radiation-type metasurface fed by a microstrip array antenna is proposed in this paper, which is used to construct a new-architecture wireless communication system. Compared to the reported metasurface-based communication systems, the proposed design is more flexible for information modulation and transmission, with the system profile significantly reduced. The phase modulation is implemented by changing the transmission phase of metasurface, allowing for baseband signals to be directly imparted to the carrier wave from the feeding source. A real-time signal transmission experiment validates the performance of the proposed metasurface-based communication system.

Orbital angular momentum (OAM) vortex waves have become a prominent topic in scientific research and engineering applications. With the developments of metasurface-based OAM generation and manipulation technologies, Huygens’ metasurfaces demonstrate the advantages of low profile and simple structure. In this paper, we propose a broadband Huygens’ metasurface capable of polarization-independent OAM-multiplexed beam deflections. Firstly, a highly efficient polarization-independent Huygens’ meta-atom is designed, and then the dual-polarized 3-bit phase profiles are constructed to generate the polarization-independent OAM-multiplexed beams. On this basis, dual-polarized phase sequences are incorporated into the 3-bit phase profiles, enabling the broadband polarization-independent OAM-multiplexed dual beam deflections in two orthogonal planes. We fabricated and measured three metasurface samples, and the experimental results are consistent with the simulations, confirming the feasibility and practicality of the proposed method. The proposed metasurface operated at 8.5 GHz-11.5 GHz, achieving a 30% relative bandwidth and 14.8% aperture efficiency. We believe this design demonstrates promising potential for applications in multi-target wireless communications and wide-range radar detections.

Metasurfaces provide an unprecedented capability for manipulating electromagnetic waves. In this study, a wideband and high-gain folded transmit-array antenna (FTA) based on a 3-bit Fabry-Perot transmission polarizer (FPTP) metasurface was proposed and realized. The proposed FTA comprises three key components: (1) top-layer FPTP metasurface, (2) bottom-layer miniaturized waveguide horn feed, and (3) reflector array. The FPTP metasurface adopts a sandwich structure, integrating two orthogonal metallic grids with an embedded 3-bit digitally encoded C-shaped ring, which simultaneously achieves polarization conversion and high-precision phase compensation while avoiding insertion losses caused by multilayer stacking. The feed employs a customized miniaturized waveguide horn, and the reflector incorporates a 90 degrees polarization conversion function, effectively mitigating the impact of missing central elements in the primary reflector without requiring additional polarization layers. Through synergistic optimization of the FPTP metasurface, feed, and reflector, the system achieves high-gain and wideband performance while maintaining a low-profile geometry (thickness reduced to one-quarter of the focal length). A prototype with 45 x 45 unit cells was fabricated and tested, demonstrating an operational bandwidth of 11.3-17 GHz, a measured peak gain of 27.1 dBi, a 3-dB gain bandwidth of 36.4%, and an aperture efficiency of 38%, all of which align closely with simulations. The proposed 3-bit FPTP metasurface provides a novel solution for low-profile, high-gain antenna design and is expected to find potential applications in next-generation wireless communication systems.

Conventional methods with one incident port are ill-suited for addressing the heightened complexity inherent in Reconfigurable metasurface (RMS) cell design. This complexity arises from the demands to accommodate multiple devices, hybrid reflection-transmission modalities, polarization manipulation, and oblique wave incidence. In response to these formidable design challenges, a universal method based on multiport scattering parameter networksis first proposed to calculate the scattering parameters of RMS cells efficiently and rapidly. It enables a comprehensive analysis of all the electromagnetic properties, including the polarization control, reflectance, transmittance, and angular sensitivity. To verify the method's versatility and accuracy, the simulated results of two distinct RMS cells and experimental results are in good with the predictions of the proposed method, demonstrating its great potential for intelligent, reconfigurable devices and system implementation.

Micro-Doppler effect is a vital feature of a target that reflects its oscillatory motions apart from bulk motion and provides an important evidence for target recognition with radars. However, establishing the micro-Doppler database poses a great challenge, since plenty of experiments are required to get the micro-Doppler signatures of different targets for the purpose of analyses and interpretations with radars, which are dramatically limited by high cost and time-consuming. Aiming to overcome these limits, a low-cost and powerful simulation platform of the micro-Doppler effects is proposed based on time-domain digital coding metasurface (TDCM). Owing to the outstanding capabilities of TDCM in generating and manipulating nonlinear harmonics during wave-matter interactions, it enables to supply rich and high-precision electromagnetic signals with multiple micro-Doppler frequencies to describe the micro-motions of different objects, which are especially favored for the training of artificial intelligence algorithms in automatic target recognition and benefit a host of applications like imaging and biosensing.

Polarization control of electromagnetic (EM) waves is vital in imaging and wireless communication systems. In this communication, we propose a broadband polarization-reconfigurable converter (BPRC) based on active metasurfaces, which can achieve polarization-reconfigurable conversion under both linear-polarization (LP) and circular-polarization (CP) incident waves in wide bands by changing the states of the p-i-n diodes. The BPRC is composed of three-layer metal patches, three-layer dielectric substrates, and p-i-n diodes. When the p-i-n diodes are in the OFF-state, the LP and CP incident waves can be converted into cross-polarization and co-polarization reflected waves, respectively. Whereas when the p-i-n diodes are changed from OFF-state to ON-state, the LP and CP incident waves can be converted into co-polarization and cross-polarization reflected waves, respectively. The conversion ratio is higher than −1 dB in the frequency range of 7.4–12 GHz, with a relative bandwidth of 47.4%. Furthermore, the simulated and experimental results were in good agreement, and thus verified the feasibility of the BPRC, which will find promising applications in wireless communication systems.

Manipulations of multiple carrier frequencies are especially important in a variety of fields like radar detection and wireless communications. In conventional radio-frequency architecture, the multi-frequency control is implemented by microwave circuits, which are hard to integrate with antenna apertures, thus bringing the problems of expensive system and high power consumption. Previous studies demonstrate the possibility to jointly control the multiple harmonics using space-time-coding digital metasurface, but suffer from the drawback of inherent harmonic entanglement. To overcome the difficulties, we propose a multi-partition asynchronous space-time-coding digital metasurface (ASTCM) to generate and manipulate multiple frequencies with more flexibility. We further establish an ASTCM-based transmitter to realize wireless communications with frequency-division multiplexing, where the metasurface is responsible for carrier-wave generations and signal modulations. The direct multi-frequency controls with ASTCM provides a new avenue to simplify the traditional wireless systems with reduced costs and low power consumption.

Polarization and phase are two essential properties of electromagnetic (EM) waves. A transmissive metasurface is proposed that can simultaneously manipulate the polarization and phase of the EM waves. The design has a powerful capability of rotating the polarization to any desired azimuth direction for a linearly polarized (LP) wave and achieving the cross‐polarization conversion for a circularly polarized (CP) wave. Meanwhile, the transmission phase of the cross‐polarization can be dynamically controlled for the CP wave. The proposed metasurface is composed of two types of substrate‐integrated waveguides (SIW) in a cross arrangement, which has an insertion loss of less than 0.3 dB from 9.7 to 10.3 GHz. Some samples are fabricated and measurements are performed, which are in satisfactory agreement with the theoretical and simulated results, indicating the feasibility of the proposed method. It is believed that the proposed design has many potential applications in the fields of imaging, communication, and radar systems.

通过对智能超表面(RIS)基本概念、方法和应用的介绍,展现了其采用数字编码方式调控电磁波各种物理特性的独特能力.深入讨论了RIS在时空域调控中的关键技术以及这些技术所衍生的示范性应用,包括成像、感知、通信与雷达等多个领域.充分展示了RIS在相关行业内的应用前景.

Recent progress in space-time-coding digital metasurface (STCM) manifests itself a powerful tool to engineer the properties of electromagnetic (EM) waves in both space and time domains, and greatly expands its capabilities from the physical manipulation to information processing. However, the current studies on STCM are focused under the synchrony frame, namely, all meta-atoms follow the same variation frequency. Here, an asynchronous STCM is proposed, where the meta-atoms are modulated by different time-coding periods. In the proposed asynchronous STCM, the phase discontinuities on traditional metasurface are replaced with the frequency discontinuities. It is shown that dynamic wavefronts can be automatically realized for both fundamental and high-order harmonics by elaborately arranging the spatial distribution of meta-atoms with various time-coding periods. The physics insight is due to the accumulated rapidly changing phase difference with time, which offers an additional degree of freedom during the wave-matter interactions. As a proof-of-principle example, an asynchronous STCM for automatic spatial scanning and dynamic scattering control is investigated. From the theory, numerical simulations, and experiments, it can be found that the proposed STCM exhibits significant potentials for applications in radars and wireless communications.

In the past few years, wireless communications based on digital coding metasurfaces have gained research interest owing to their simplified architectures and low cost. However, in most of the metasurface-based wireless systems, a single-polarization scenario is used, limiting the channel capacities. To solve the problem, multiplexing methods have been adopted, but the system complexity is inevitably increased. Here, a space-frequency-polarization-division multiplexed wireless communication system is proposed using an anisotropic space-time-coding digital metasurface. By separately designing time-varying control voltage sequences for differently oriented varactor diodes integrated on the metasurface, we achieve frequency-polarization-division multiplexed modulations. By further introducing different time-delay gradients to the control voltage sequences in two polarization directions, we successfully obtain space-frequency-polarization-division multiplexed modulations to realize a wireless communication system with a new architecture. The new communication system is designed with compact dual-polarized meta-elements, and can improve channel capacity and space utilization. Experimental results demonstrate the high-performance and real-time transmission capability of the proposed communication system, confirming its potential application in multiple-user collaborative wireless communications.

Reconfigurable intelligent surface (RIS) and index modulation (IM) are two emerging technologies, which show great potentials to achieve green and clean wireless communications, attracting extensive attention in recent years. This paper designs and implements an RIS-based IM transmission scheme that effectively integrates the two techniques. By utilizing the characteristics of RIS to realize flexible control of electromagnetic waves in a reconfigurable manner, IM wireless transmission can be directly realized without conventional radio frequency chains. The proposed approach is validated through the prototype system which is set up based on a fabricated phase-programmable RIS operating in the sub-6GHz frequency band. The experimental results convincingly verify the feasibility of the proposed scheme and suggest that RISs offer a cost-effective hardware architecture to realize IM with massive transmitting antennas.

The rapid development of the reconfigurable intelligent surface (RIS) technology has given rise to a new paradigm of wireless trans-mitters. At present, most research works on RIS-based transmitters focus on single-polarized RISs. In this paper, we propose a dual-polarized RIS-based transmitter, which realizes 4-transmit space-time block coding (STBC) transmission by properly partitioning RIS's unit cells and utilizing the degree of freedom of polarization. The proposed scheme is evaluated through a prototype system that utilizes a fabricated dual-polarized phase-adjustable RIS. In particular, the polarization coupling phenomenon in each unit cell of the employed dual-polarized RIS is modeled and analyzed. The experimental results are in good agreement with the theoretical modeling and analysis results, and an initial re-search effort is made on characterizing the polarization coupling property in the dual-polarized RIS.

In general, direction of arrival (DOA) estimation requires massive receiving antennas with independent transceivers, which brings expensive hardware and large power consumption. In this paper, we propose a novel method to realize DOA estimation using an asynchronous space-time-coding digital metasurface (ASTCM). Compared with the classic methods implemented with conventional phased arrays, the metasurfacebased DOA estimation can be realized without massive transceivers, which greatly simplifies the physical architectures and cuts the hardware cost. In addition, since the ASTCM is capable of creating a frequency gradient across the metasurface, the reflected signals will carry natural orthogonality in the frequency domain. Based on this, the DOA information can be directly extracted from the spectrum. We demonstrate the feasibility of the proposed method through theoretical deduction and simulated calculation. It may have great potential in wireless communications and the Internet of Things.

We present a C-band amplifying reconfigurable intelligent surface (ARIS) integrated with power amplifier (PA) to enhance the reflected electromagnetic (EM) signals. An aperture-coupled patch element with two orthogonal hourglass-shaped slots is elaborately constructed to ensure a broad operation bandwidth. A power combining and dividing network is also introduced to combine the 2 $\times2$ elements into a subarray to reduce the number of PAs and the system cost. The simulation results indicate that the achieved gain of ARIS is 7.7–12.2 dB from 5.0 to 6.0 GHz. A prototype of the proposed ARIS is designed, fabricated, and experimentally verified. The measured results agree well with the simulation. The proposed ARIS is promising for applications in future wireless communication systems for signal enhancement and coverage extension.

The polarizations of electromagnetic (EM) waves are very important for transceivers. We propose a broadband polarization-insensitive polarization rotator (PIPR), which can realize 90° polarization rotation for incident waves with an arbitrary azimuth angle. A unit of the PIPR is composed of two types of substrate integrated waveguide (SIW) units in a checkerboard pattern, which provides more than -0.2 dB transmission from 9.5 to 10.9 GHz. The electric field inside the cavity is analyzed to explain the working mechanism of the proposed rotator. A prototype is fabricated and measured to verify the proposed design, and satisfactory agreement between simulated and measured results is achieved, indicating that the converter has potential applications in imaging and communication systems.

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.

The rapid development of space-time-coding metasurfaces (STCMs) offers a new avenue to manipulate spatial electromagnetic beams, waveforms, and frequency spectra simultaneously with high efficiency. To date, most studies are primarily focused on harmonic generations and independent controls of finite-order harmonics and their spatial waves, but the manipulations of continuously temporal waveforms that include much rich frequency spectral components are still limited in both theory and experiment based on STCM. Here, we propose a theoretical framework and method to generate frequency-modulated continuous waves (FMCWs) and control their spatial propagation behaviors simultaneously via a novel STCM with nonlinearly periodic phases. Since the carrier frequency of FMCW changes with time rapidly, we can produce customized time-varying reflection phases at will by the required FMCW under the illumination of a monochromatic wave. More importantly, the propagation directions of the time-varying beams can be controlled by encoding the metasurface with different initial phase gradients. A programmable STCM prototype with a full-phase range is designed and fabricated to realize reprogrammable FMCW functions, and experimental results show good agreement with the theoretical analyses.