This work presents a novel single-layer, reconfigurable spatial power splitter based on plasma discharges. Each unit cell features two adjacent core–shell cylinders, composed of a tunable plasma core surrounded by a high-permittivity dielectric shell. The plasma core is modeled using a free-electron plasma permittivity with variable plasma frequency. Numerical simulation demonstrates that the power-splitting ratio can be continuously varied between 30% and 70% by independently controlling the plasma frequencies of the two cylinders. This reconfigurability enables precise manipulation of the transmitted power distribution while limiting the total reflected, absorbed, and undesired diffraction power to less than 10% of the incident energy, corresponding to an overall efficiency exceeding 90%.

The classical analytical formulation of 2-D Mie scattering for coaxial cylindrical multilayers requires solving a 2Nx2N system of equations for each polarization, where N is the number of layers, which quickly becomes cumbersome as N increases. In this letter, we address this challenge by developing a compact recursive approach, based on Richmond's 1965 method for dielectric shells, reformulated as a sequence of simple 2x2 systems. We extend Richmond's formulation to the case of multilayer impedance boundaries (e.g., metasurfaces), making it particularly effective for modern scattering engineering problems, such as metasurface cloaking design. The effectiveness of the approach is demonstrated through the minimization of the scattering signature of a metallic cylinder surrounded by such multilayer impedance surfaces. The results are validated against independent full-wave electromagnetic simulations.

Benefiting from the precise electromagnetic (EM) wave manipulation capability of metasurface (MTS), MTS-based EM tags exhibit significant potential for advancement in the field of radio frequency identification (RFID). This article presents the theoretical analysis, design, and experimental verification of an MTS-based tag employing spatial-frequency coding. Unlike conventional RFID tags and prior MTS-based tags, the proposed tag is an active MTS-based identification platform integrating phase modulation circuits, power amplifiers (PAs), and polarization conversion antennas. By exploiting these functionalities, the tag modulates the interrogation signal to generate tunable harmonics, whose spatial combinations encode the tag information. The backscattered response is further polarization-converted and amplified, rendering it cross-polarized with respect to environmental clutter and extending the read range. An X-band prototype is fabricated, featuring a 700-MHz bandwidth and a 10-dB enhancement in backscattered power compared to a metallic plate of the same aperture. Experiments under strong reflection and long read range conditions verify the feasibility of the proposed tag.

Radar target characteristic deception is a core technology in modern electronic countermeasures (ECM), designed to systematically mislead radar detection, tracking, and recognition systems. As radars hardware and signal processing algorithms become increasingly sophisticated, traditional deception technologies struggle to meet the requirements for low power consumption, and synchronous, multi-dimensional regulation. Programmable metasurfaces offer a transformative solution through their unique ability to achieve flexible and precise electromagnetic (EM) waves manipulation across multiple domains. By leveraging programmable EM responses, these artificial surfaces provide an innovative, low-complexity pathway for high-performance multi-dimensional target characteristic deception. This review provides a comprehensive synthesis of the research progress in metasurfaces-enabled radar deception, covering critical areas such as 1-D high-resolution range profiles (HRRPs), range-Doppler profiles, micro-Doppler signatures, 2D synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) profiles. Moreover, the article discusses emerging perspectives, future visions, and potential evolutionary trajectories for this research field. By providing a holistic reference for researchers, this review aims to bridge the gap between theoretical metasurface design and the practical application of metasurface-enabled deception technologies in modern ECM systems.

This contribution presents and discusses the electromagnetic functionalities achievable through the application of diverse Space-Time (ST) modulation schemes to reconfigurable metasurfaces. We analyze the simplest configuration-binary coding-which relies on only two discrete states in amplitude and/or phase to control the surface properties. Three distinct classes of ST modulation schemes are examined via theoretical analysis and experimental validation. The results demonstrate that a single metasurface can deliver a broad range of diverse and specialized functionalities merely by dynamically altering the applied ST scheme. Specifically, we showcase the utility of unconventional ST patterns, including quasi-periodic profiles with engineered time delays, entirely random aperiodic distributions, and aperiodic profiles.

This communication presents the theory and design of a joint fast-and-slow time modulation for space-time-modulated metasurfaces (ST-MTSs) to simultaneously and precisely generate 1-D high-resolution range profile (HRRP), range-Doppler profile, and micro-Doppler signature. The design process is guided via scattering center model of the deceptive target to be reproduced by the stationary metasurface. To achieve such a multiradar-characteristics jamming, fast-time modulation is implemented to generate deceptive HRRPs, whereas extra phase terms are introduced in slow-time domain to compensate for the phase differences between adjacent pulses in the echo caused by the motion and micromotion of the deceptive target. For precise jamming, the scattered electromagnetic (EM) field of a deceptive target is first expressed to derive the radar multicharacteristics with the help of scattering center models. A vector analysis in the complex plane is then employed to synthesize the amplitude-phase reconfigurable reflection coefficients using a 2-bit phase reconfigurable metasurface, further improving the performance of the jamming method. Both numerical simulations and experimental results confirm the effectiveness of the proposed jamming method.

Reconfigurable metasurfaces represent a key enabling technology for next-generation programmable electromagnetic environments. However, most existing solutions rely on active biasing networks, via-based architectures, or reflective configurations, which limit their scalability and practical deployment. In this work, we present a design framework for self-reconfigurable pulse-driven Huygens’ metasurfaces operating in transmission mode and enabling self-reconfigurable beam steering functionalities without external biasing networks. The proposed metasurface exploits the transient electromagnetic response of waveform-selective nonlinear circuits embedded within multilayer Huygens unit cells, allowing the phase gradient of the surface to be autonomously reconfigured depending on the temporal waveform of the impinging signal. A hybrid synthesis workflow is introduced, combining an analytical microwave-matrix-based model for the ideal phase-gradient metasurface with a mixed deterministic and multi-objective optimization strategy for the realistic unit-cell implementation. The approach enables the realization of planar transmissive Huygens’ metasurfaces consisting of via-less multilayer cells compatible with standard PCB technologies. Full-wave numerical simulations demonstrate pulse-dependent beam steering, with the steering functionality enabled for short-pulse excitations and suppressed for continuous-wave signals. The proposed methodology provides a scalable and bias-free solution for programmable transmissive metasurfaces and reconfigurable intelligent surface applications.

This contribution presents a reconfigurable metasurface for enhancing the beam-steering capabilities of sparse antenna arrays while preserving broadside transparency. The proposed metasurface consists of unit cells composed of three stacked ideal impedance layers, whose surface reactances are optimized to achieve two operational states: in the OFF state, an obliquely incident wave from a sparse array is steered toward a larger angle, whereas in the ON state, a normally-incident wave passes through with negligible insertion loss. The unit-cell design is based on an analytical microwave matrix model, which provides an initial guess for a multi-objective full-wave optimization accounting for inter-cell coupling and non-local effects. Full-wave results show that the metasurface effectively extends the scanning range of a sparse array from 30° to 60° without introducing grating lobes, while maintaining the broadside gain when in the ON state.

Reflection-type time-modulated metasurfaces are designed to exhibit a complex reflection coefficient that varies in time, assuming a discrete number of reflection states. To maintain high efficiency, the metasurface is designed to have unitary amplitude and a discrete number of phase levels, with ideal abrupt transition from one phase state to another when the modulation is present. However, the overall reflection coefficient is affected by the rise/fall time of the control voltage, shifting away the overall response of the metasurface from the ideal one. In this article, we present a microwave-network-based method that allows speeding up the analysis and optimization of time-modulated metasurface in the presence of nonideal temporal modulation. Additionally, the proposed method speeds up the calculation for the scattering field from the metasurface, maintaining a high level of accuracy and reduced computational efforts. To validate its effectiveness, linear phase modulation and in-phase and quadrature (I-Q) modulation are considered for achieving single sideband (SSB) modulation of the illuminating signal. Both numerical and experimental results confirm the accuracy of the microwave-network-based method in estimating the reflection spectrum emerging from the metasurface. Additionally, after optimization, the harmonic generation is improved by 12% for the linear phase modulation and 7% for the I-Q modulation. These outcomes demonstrate the reliability and practicality of the entire approach.

The dispersion features of the line wave supported by a double-layer line-wave waveguide with a cross section exhibiting central symmetry are determined through full-wave simulations of a truncated structure and a numerical post-processing fitting procedure. Within the low-frequency homog-enization regime, in which the unit cell of the constituent metasurfaces is a small fraction of the free-space wavelength, the phase constant of the line wave is thus retrieved rigorously. The adopted approach has been also extended to higher frequencies beyond the homogenization limit, where higher order space harmonics become non-negligible, the line wave is thus to be regarded as a Bloch mode of a periodic structure, and the associated stopband regimes are shown to emerge.

In this article, we review some of the recent efforts and advancements in the implementation of reconfigurable metasurfaces and metamaterials tailored for antenna applications. Originally limited by fixed properties, these structures are increasingly integrated with different technologies to achieve real-time reconfigurability and versatility in response to evolving operational conditions and constraints. This work investigates the motivations and technical approaches driving this development, with a specific focus on reconfigurable metasurfaces designed for antenna systems operating within the microwave range (L-band to K-band). By analyzing limitations and experimentally validated approaches, the article offers a comprehensive exploration of the performance and limitations of common reconfigurability schemes in microwave metadevices.

This paper investigates the optimization of cylindrical metasurface meta-covers designed to enable beamforming capabilities in single linear antennas. This study focuses on the development and application of advanced optimization tools to tailor the electromagnetic response of these metasurfaces, enabling precise control over the radiation patterns of the antenna. In particular, we develop a genetic algorithm-based optimization tool, which achieves precise manipulation of the main beam direction and null placement in the radiation pattern. The results further expand the applications of metasurface-based meta-covers in enhancing the functionality of dipole antennas in various communication and sensing systems.

Time-modulated metasurface can serve as a spoofing cloak partially covering on a static real target, thereby generating false targets in the high-resolution range profile (HRRP) and making the real target undetectable. This article proposes an electronic counter-countermeasure (ECCM) detection method to nullify the spoofing capabilities of time-modulated metasurfaces. The proposed method utilizes pseudorandom-coded (PC) radar signals that exhibit range-Doppler uncoupling characteristics, allowing for the preservation of static real targets while effectively suppressing false targets in the HRRP. Here, we first analyze the impact of the time-modulated metasurface on the reflected conventional linear frequency-modulated (LFM) signal and the proposed PC signal by using the 2-D correlation results (CRs) as a function of the time delay and Doppler shift. This analysis demonstrates how the range-Doppler coupling plays a role in the spoofing technique implemented by the metasurface. Then, the method's effectiveness is experimentally verified using a 1-bit phase reconfigurable metasurface operating at 30 GHz. The results show that the PC radar signal significantly outperformed the LFM signal in suppressing false targets, making the real target well-detectable in the HRRP.

This contribution introduces the Composite Vortex Theory (CVT) and its application to simplified reconfiguration strategies for reflective and transmissive metasurfaces. By exploiting the unique properties of vortex fields, CVT enables efficient electromagnetic wave control with minimal structural changes to the metasurface. The proposed reconfiguration strategies simplify the design and implementation of metasurfaces for applications such as beam steering and wavefront shaping, offering a flexible and efficient solution for next-generation electromagnetic devices.

Reconfigurable and programmable metasurfaces require reliable strategies for dynamic control of their electromagnetic response. Among the approaches explored so far, low-temperature plasma is particularly attractive thanks to its tunable permittivity, which can be adjusted in real time via electron density modulation. Despite this potential, quantitative experimental validation at microwave frequencies has remained limited. In this work, we present a comprehensive characterization of plasma tubes as reconfigurable building blocks for metasurface architectures. Using a custom waveguide measurement setup, we retrieve key plasma parameters-such as electron density and plasma frequency-under varying excitation conditions. These measurements are complemented by multiphysics plasma simulations, full-wave electromagnetic modeling, and circuit-level electrical diagnostics, ensuring cross-validation across independent methodologies. Our results demonstrate a continuous and controllable tunability of the plasma response, with electron densities reaching the range. The close agreement between experiments, models, and simulations confirms the feasibility of integrating plasma elements into adaptive metasurfaces. This study establishes plasma tubes as viable dynamic meta-atoms, paving the way toward high-power, high-speed, and fully reconfigurable microwave systems.

Transmissive metasurfaces-based on the coexcitation of electric and magnetic responses-enable full control of electromagnetic waves in transmission, making them ideal candidates for advanced beam-steering applications. These metasurfaces, often referred to as Huygens' metasurfaces, allow precise manipulation of phase and amplitude while maintaining high transmission efficiency. When integrated with radiating systems such as antennas and phased arrays, they unlock novel functionalities, including beam shaping without complex feeding networks and enhanced angular scanning capabilities. This contribution explores the potential of transmissive metasurfaces in modern antenna systems, highlighting their role in shaping radiated fields and extending system-level performance beyond traditional limits.

The massive scale of Internet of Things (IoT) connectivity expected in 6G networks raises unprecedented challenges in energy use, battery waste, and lifecycle sustainability. Current cellular IoT solutions remain bound to the lifetime of underlying network generations and rely on billions of disposable batteries, creating unsustainable economic and environmental costs. This article proposes generation-agnostic zero-energy devices (XG-ZEDs), a new class of backscatter based IoT devices that are battery-less, spectrum-agnostic, and future-proof across successive network generations. XG-ZEDs exploit existing ambient wireless signals for communication, sensing, and localization, transforming infrastructure and user devices into universal enablers of ultra-low-power connectivity. We review architectural classifications, communication protocols, network integration, and representative applications such as sensing, localization, and radio-SLAM, while outlining the challenges ahead.

A theoretical framework is developed to propose single- and dual-band mantle cloaks composed of low-profile single-layer electrically and magnetically polarizable (EMP) metasurfaces. The target is a dielectric cylinder with a circular cross-section. The metasurface immitances are modeled by Lorentzian functions to model the near-resonance behavior of realistic unit cells. For small targets, to suppress the dominant zeroth-order scattered harmonic, closed-form and semi-closed-form relations are derived for Lorentzian parameters to achieve dual-band and single-band operations, respectively. Compared to pure electric cloaks, the scattering efficiency (SE) for the single-band electric-magnetic cloak experiences a 12 dB improvement, and the cloaking bandwidth is nearly doubled at 350 THz. For larger targets with two significant scattered modes, a semi-analytical approach is developed. Accordingly, compared to a double-layer electric cloak of the same thickness, an improvement of about 7.5 dB in SE and a fivefold bandwidth enhancement at 500 THz are achieved. The proposed modal solution is verified by the method of moments (MoM). EMP metasurfaces mimic the behavior of dielectric metasurfaces, which are necessary for THz and optical bands due to their low loss.

In this letter, we propose a novel single-layer reconfigurable transmissive metagrating based on plasma discharges. Each unit-cell consists of two side-by-side core-shell cylinders, with a tunable plasma core and a high-index dielectric shell. The structure is modeled using a free-electron plasma permittivity with an adjustable plasma frequency. Analytical and numerical results show that the main transmission lobe can be switched between -41 degrees, 0 degrees, and 41 degrees by tuning the plasma frequencies. Transmission efficiency remains above 80% at broadside and 90% in the steered direction. This tunability enables effective directional control with low reflection and high overall power efficiency.