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The convergence of integrated sensing and communications (ISAC) with reconfigurable intelligent surfaces (RIS) and metasurface-based architectures is emerging as a key direction for sixth-generation (6G) wireless networks, supporting joint communication and sensing through programmable electromagnetic environments. This survey provides an integrated treatment of metasurface-empowered ISAC across terrestrial, airborne, and spaceborne tiers. Six metasurface architectures are covered: passive and active RIS, simultaneously transmitting and reflecting RIS (STAR-RIS), space-time-coding metasurfaces (STCM), holographic multiple-input multiple-output (MIMO) surfaces (HMIMOS) and the closely related stacked intelligent metasurface (SIM), and metasurface reflectarrays that generate orbital angular momentum (OAM) beams. The survey reviews the electromagnetic foundations, channel models, ISAC waveform design, and performance bounds, then synthesises the terrestrial pillar across beamforming, resource allocation, hardware impairments, and energy efficiency. The OAM-ISAC pillar examines how vortex beams provide additional degrees of freedom for rotational sensing, while critically assessing the practical mode limits and maturity gaps. The non-terrestrial pillar addresses low Earth orbit (LEO) satellites, high-altitude platform stations (HAPS), and unmanned aerial vehicles (UAVs), covering link-budget, Doppler, and handover challenges. Cross-cutting enablers, namely artificial intelligence (AI) driven optimisation and physical-layer security, are surveyed with emphasis on their interplay with metasurface-ISAC. Two assumptions that pervade the surveyed optimisation literature, perfect instantaneous channel state information and cost-free channel acquisition, are examined critically: a coherence-time-aware accounting of pilot overhead, illustrated by an anchored numerical sensitivity analysis, shows that the reported multiplexing and sensing gains of large surfaces are bounded by the associated acquisition costs. The 3GPP, ETSI, ITU-R, and O-RAN standardisation status frames the route to deployment. Fifteen prioritised open challenges and a technology roadmap to 2035 complete the treatment. By bridging the electromagnetic, signal-processing, and networking communities, this work aims to serve as a reference for researchers and engineers shaping 6G ISAC.

Lateral surface-wave coupling between branches of a corporate microstrip feeding network often limits the efficiency of millimetre-wave planar arrays. Current feed-network mit-igations, such as substrate-integrated waveguides and printed ridge-gap waveguides, require complex multilayer stack-ups or altered line cross-sections. Conversely, radiator-side techniques like electromagnetic band gaps and parasitic stripes leave feed-network losses unaffected. To address this gap, we propose a feature-graded ground stripe that interacts directly with the feed network on a single metallic layer. By using grounded auxiliary stripes and plated metallic vias, this design creates a robust isolation barrier between feeding branches to drain laterally propagating surface-waves before they can recouple. We integrated this approach into an eight-element rectangular dielectric resonator antenna (DRA) array specifically tailored for the 3GPP n257 band. The resulting array delivers a-10 dB bandwidth spanning 25.77 to 28.83 GHz (fractional bandwidth of 11.2%). Furthermore, it achieves a peak realised gain of 18.6 dBi at 28.2 GHz alongside a total efficiency exceeding 90% between 27.0 and 28.5 GHz. Inter-branch isolation (S23) is maintained below-33 dB across the operational band. Finally, experimental validation of a fabricated prototype shows that the measured reflection coefficient (S11) confirms the design's practical viability.

Line-waves (LWs) are highly confined one-dimensional electromagnetic modes that propagate along the interface between complementary metasurfaces and offer a promising platform for overcoming the inherent limitations of conventional power dividers. Traditional structures, such as Wilkinson power dividers, often suffer from narrow bandwidth, high insertion loss, and limited power handling capability, which restrict their performance in modern radio frequency (RF) and microwave systems. In this work, we propose a compact topolog-ical T-shaped (1×2) power divider that leverages complementary inductive–capacitive metasurfaces in conjunction with dielectric loading. The complementary metasurfaces enable the coexistence of TM and TE surface modes, while the dielectric loading significantly enhances field confinement and impedance matching across a broad frequency range. Therefore, the proposed design achieves low loss, high power transfer efficiency, and broadband operation. The presented structure offers a scalable solution that addresses key challenges in RF and microwave circuitry, providing an effective approach for next-generation signal distribution networks.

Aperiodic element distributions can reduce reflectarray cost and weight by 35%, but they introduce two problems absent in periodic designs: (i) the required phases uniformly span the full 360â—¦, demanding wider S-curve coverage than a single-parameter element typically provides, and (ii) non-uniform inter-element spacing causes physical overlaps when variable-size patches are used. This paper addresses both problems through a proportionally notch-loaded rectangular patch element at 28 GHz. The element has a fixed width Wp = 2.5 mm, variable length Lp, and two symmetric notches of depth d n = 0.15Lp on the non-radiating edges, yielding 336â—¦ of phase range with 211â—¦ of independent fine tuning on 0.508 mm Rogers RO4003C substrate. Combined with a stealthy hyperuniform distribution on a 120 mm diameter circular aperture, the design achieves 19.7 dBi realised gain at 27 GHz with 287 elements, 0.2 dB above a 441-element periodic reference, while using 35% fewer elements and exhibiting 0.3 dB lower sidelobes. To the authors' knowledge, this is the first reflectarray to combine a proportional notch-loaded element with a hyperuniform distribution at millimetre-wave frequencies.

Integrated Sensing and Communication (ISAC) is pivotal to the development of Sixth Generation (6G) wireless systems, seamlessly merging communication and sensing capabilities to optimise both spectral and hardware resources. The incorporation of Orbital Angular Momentum (OAM) presents a significant opportunity to enhance ISAC by boosting spectral efficiency and facilitating advanced spatial multiplexing techniques. This paper explores the synergies between OAM and other state-of-the-art technologies, including Millimetre-Wave (mmWave)/Terahertz (THz) communications, ultra-massive MIMO (umMIMO), and Reconfigurable Intelligent Surfaces (RIS). We aim to explore the collaborative potential of OAM-enabled ISAC in conjunction with emerging wireless technologies, positioning them within the broader landscape of 6G communications and beyond.

—We introduce a novel topological valley photonic crystal antenna, designed on a silicon-on-insulator platform, operating at 193.5 THz with the efficiency of 80%. By lever-aging the unique properties of valley-polarized edge modes, this antenna achieves robust and efficient radiation, exceptional resilience to structural imperfections, and precise control over light propagation. The proposed design exemplifies high-performance capabilities, marking a significant leap forward in the integration of topological photonics. This breakthrough opens new horizons for next-generation optical communication systems, advanced sensing technologies, and other transformative photonic applications.

—This paper proposes a novel Integrated Sensing and Communication (ISAC) metasurface designed to operate at 29.5 GHz. It leverages a Reflectarray Antenna (RA) capable of supporting dual functionalities—pencil beamforming for high-speed communication and Orbital Angular Momentum (OAM) beams for precise sensing. The communication aspect employs a pencil beam configuration to achieve high gain focused and directional transmission, while the OAM beam enables enhanced spatial resolution for sensing applications. Extensive simulations and lab measurements validate the superior performance of this single RA system, demonstrating improved gain and OAM beam purity metrics. This ISAC approach has the potential to reduce system complexity by 50% and energy consumption by 80% through a passive antenna design that facilitates both communication and sensing functionalities. Index Terms—6G, integrated sensing and communication, reflectarray antenna, orbital angular momentum.

This paper presents a novel on-chip hybrid plas-monic leaky-wave nanoantenna, enhanced by optical transverse periodic slots, designed for the standard telecommunications wavelength of 1550 nm. By leveraging the combined advantages of hybrid plasmonic waveguides and leaky-wave mechanisms, this nanoantenna achieves superior light confinement and highly directive radiation patterns. The multi-layer structure, featuring InGaAsP, gold, and quartz, ensures minimal propagation loss and efficient mode conversion from guided to radiative modes. Simulation results demonstrate the antenna's performance with a directivity of 18.5 dBi and a gain of 14.3 dBi, while maintaining a low side-lobe level and broad bandwidth. These characteristics make it highly suitable for integrated optical interconnects, beam-steering devices, and enhanced solar cells. The design is fully compatible with standard complementary metal-oxide-semiconductor (CMOS) processes, facilitating seamless integration into opto-electronic circuits. This advancement marks a significant step towards highly efficient, miniaturized optical communication systems and on-chip photonic applications.

The proposed intelligent reflective surface (IRS) is presented to compensate for the path loss and enhance the coverage of 5G networks at mm-wave band. A(π) shaped element with variable-sized dipoles, distributed in a certain way to maintain a phase length curve over 340° in the range of 23-27 GHz, is addressed in this work. The proposed structure can be an ideal candidate for 5G mm-wave band n258.