Experimental demonstration of enormous fluid antenna system for future intelligent wireless systems

1 Introduction

The global deployment of fifth generation (5G) networks has spurred the development of sixth generation (6G) communications, which are anticipated to meet the demands for vast data rates, stringent reliability, and minimal latency (Dang et al., 2020), (Jia, 2023). Achieving these ambitious goals will likely require the utilization of higher frequency bands. However, operating at these frequencies inherently deteriorates wireless propagation performance, leading to issues such as increased signal attenuation through obstacles, limited coverage, and high sensitivity to environmental conditions.

Reconfigurable Intelligent Surface (RIS) technology is widely recognized as a promising solution because of its capability to intelligently reshape the wireless propagation environment and deliver substantial performance gains (Liaskos et al., 2018; Huang et al., 2019; Basar and Vincent Poor, 2021; Liu R. et al., 2025; Wu et al., 2022; Wang et al., 2021; Liu Y. H. et al., 2025). A major challenge, however, is the inherent complexity involved in optimizing the configuration of both active and passive elements within large-scale networks (Liu R. et al., 2025; Wu et al., 2022; Wang et al., 2021; Liu Y. H. et al., 2025), where the path loss for over-the-air links remains a limiting factor.

In contrast, surface wave communication focuses on exploiting guided electromagnetic waves along engineered surfaces to create new “superhighways” for wireless links in future smart radio environments and 6G systems. These surface waves, which are tightly bound to a dielectric-clad conducting platforms, offer a transformative alternative to conventional space-wave propagation. While conventional wireless links suffer from high propagation loss, reconfigurable surface-wave platforms have recently demonstrated remarkably low-loss performance. This enables signals to bend around corners, mitigate shadowing, and serve users in non-line-of-sight conditions through the use of reconfigurable intelligent surfaces and metasurfaces (Wan et al., 2019), (An et al., 2025). Building on this foundation, reconfigurable surface-wave platforms with low-loss (insertion loss is around 0.1 dB/m) controllable pathways and junctions are being reported. These systems allow power and frequency to be dynamically partitioned among multiple devices, paving the way for programmable surfaces that integrate communication within compact millimeter-wave hardware (Chu et al., 2024a), (Chu et al., 2024b). To maintain the conciseness the paper, the authors suggest that the audience can read the relevant fundamental theories in the two references.

These challenges have motivated the emergence of Fluid Antenna System (FAS) (Wong et al., 2022; Wong et al., 2020; New et al., 2025; Lu et al., 2025; Borda-Fortuny et al., 2019; Dash et al., 2023; Tong et al., 2025). FAS, which is defined as antennas that have no fixed radiation position and radiation aperture (Wong et al., 2022; Wong et al., 2020) and embodies a concept for an integrated physical-layer system empowered by antennas with reconfigurable geometry and position. The core principle of FAS is to break the traditional link between a fixed antenna structure and its electromagnetic properties (Borda-Fortuny et al., 2019; Dash et al., 2023). This functionality promotes advanced adaptive techniques such as spatial multiplexing and diversity gain.

These efficiency gains have motivated the emergence of the Fluid Antenna System (FAS), which utilizes antennas with no fixed radiation position or aperture to exploit the spatial dimension of wireless channels. Various FAS implementations have been realized in various forms (Tong et al., 2025), all leveraging reconfigurability to exploit the spatial dimension of wireless channels:

Liquid-Metal Fluid Antennas (LM-FAS): These utilize conductive non-toxic liquid metals like Galinstan or EGaIn within microfluidic channels. By physically changing the antenna’s radiating element shape or position, the system dynamically alters its radiation characteristics or effective location (Shen et al., 2026; Martinez et al., 2022).

Mechanically Movable Antennas (MMA-FAS): This implementation repositions the physical antenna element using mechanical actuators, such as stepper motors (Dong et al., 2026). However, the system’s response time to dynamic wireless channels and hardware maintenance requirements pose major concerns for practical applications.

Pixel Reconfigurable Antennas (PRA-FAS): Radiation aperture flexibility is achieved by structuring the antenna with numerous small, switchable patches or pixels. Electronically switching these pixels on or off dynamically reconfigures the effective aperture and radiation pattern, providing the benefit of position-switching without physical movement (Liu et al., 2025c; Zhang et al., 2025).

Meta-Fluid Antennas (M-FAS): This integrates a reconfigurable antenna with a coding-on-metasurface technique. By using a slot-array antenna with tunable elements (often controlled by PIN diodes), a programmable radiating aperture is created, allowing for fine spatial resolution and enhanced communication performance (Liu et al., 2025d; Liu, 2025).

Pinching Antennas (PAs): These are a type of leaky-wave fluid antenna that uses a movable element (usually a clothespin) on a dielectric waveguide to locally trigger the emission of an electromagnetic wave, offering a flexible and low-cost approach to position-reconfigurable systems (Fukuda et al., 2022).

This paper presents the first experimental demonstration of an enormous reconfigurable surface (Wong et al., 2021; Tong and Wong, 2023). This surface is designed to function not only as a smart propagation medium but also as a smart radiator. High-efficiency signal transmission is achieved by guiding electromagnetic (EM) waves along a surface wave channel, substantially replacing conventional over-the-air propagation. When the surface wave reaches a target location, a launcher is created by configuring specific cavity state distributions, which then efficiently emits the signal into free space. This concept is referred to Enormous FAS in this manuscript, and it is intended to inspire the development of next-generation reconfigurable antenna technologies.

2 Design principles and systems

Traditional wireless communication, which relies on multiple reflections of radio waves in free space for non-line-of-sight communication, suffers from high propagation loss and limited coverage. To address these limitations, we investigate an E-FAS designed to replace a significant portion of conventional over-the-air transmission with surface wave propagation.

As illustrated in Figure 1a, the proposed Enormous FAS is implemented on a reconfigurable porous surface, while the feeder consists of a rectangular coaxial-to-waveguide adaptor machined from an aluminum block with a horn-shaped air cavity to excite surface waves. The operation of the Enormous Fluid Antenna System (E-FAS) relies on the precise manipulation of Transverse Magnetic (TM) surface waves, specifically the T M 0 mode, which are guided along the dielectric-clad conducting ground plane. The propagation constant of these waves, β s w, is fundamentally determined by the surface reactance X s of the dielectric layer, such that β s w = k 0 1 + X s / η 0 2, where k 0 represents the free-space wavenumber and η 0 is the intrinsic impedance. By utilizing the F4BM-2 substrate (F4BM, 2026), which exhibits a stable dielectric constant of 2.2 and a low dissipation factor of 0.001 at millimeter-wave frequencies, the surface wave platform can operate −50 °C∼+260 °C with low moisture absorption less than 0.09% change when dip in 20 °C distilled water for 24 h. The hollow cylindrical cavities, spaced at a sub-wavelength interval of 1.2 mm, function as localized impedance tuners; the transition from an air-filled off-state to a metal-filled on-state creates a significant boundary condition shift, effectively perturbing the guided wave into a leaky wave for high-gain radiation. This reconfigurability allows for the dynamic formation of surface wave with low insertion loss of approximately 0.1 dB/m, which is an improvement over the signal attenuation typically observed in free-space propagation at these frequencies.

As shown in Figure 1b, each cavity can be switched between the on-state (metal-filled) and the off-state (air-filled) by inserting or removing a metal rod of the same radius and length as the cavity (An et al., 2025; Chu et al., 2024a), thereby enabling flexible surface-wave propagation and radiation from specific positions. The on- and off-states of the cavities can also be achieved by connecting electronic devices, such as PIN diodes, between the metal rods and the ground plane. The model of a unit cell with a PIN diode is depicted in Figure 1c. Isolating slots are used to separate the ground and the metal rods to achieve off-state. When switching to on-state, the control unit, such as FPGA or MCU, will forward-bias the PIN diodes to connect to metal robs to the ground, then a guided structure is created. Switching speed, which mainly depends on the control modules and the electronic devices used, ranges from a few microseconds to nanoseconds (GaAs, 2026; Agilex, 2026).

The switching speed of FAS is fundamentally limited by the semiconductor physics of the switching elements and the control logic speed. PIN diodes facilitate the cavity state transition through the injection of carriers into the intrinsic region; during the turn-on phase, the transition from a high-impedance state to a low-impedance state is governed by the carrier lifetime τ and the time required to establish a conductive plasma across the I-layer. The forward-bias resistance R s is inversely proportional to the injected current I f, approximately defined as R s ≈ W 2 / 2 μ I f τ, where W is the I-region thickness and μ is the carrier mobility. Furthermore, the overall system response time is affected by the control module, such as a high-end MCU or FPGA, which introduces latency through GPIO toggle speeds and propagation delays within the PCB traces. For high-frequency applications, the parasitic inductance L p and capacitance C p of the diode packaging can be compensated to ensure nanosecond-scale switching, preventing signal reflections during the transient states.

The surface-wave channel is formed by configuring two rows of cavities in the on-state, as shown in Figure 1d. Similar to conventional metal waveguides with the width of the channel determines the operating frequency. Furthermore, by adjusting the channel pathway, the signal can be manipulated to different position. The simulated E-field distribution of the proposed design is depicted in Figure 2a, the surface wave generated by the feeder remains confined within the defined path, achieving high-efficiency isolated propagation. It should be noted that the space wave incurs at the feeder-to-open-space interface can be minimized by a proper designed feeder (Wan et al., 2019). The surface wave continues to propagate along the surface wave channel to desired position.

To radiate the signal into free space once it reaches the desired position, a surface-wave launcher is utilized. As demonstrated in Figure 1e, the surface wave launcher, composing of two ±45° lines of 1 × 8 on-state cavities and a 7 × 10 rectangular array of on-state cavities, is realized. In this structure, the on-state cavities act as scatterers that gradually leak energy as the surface wave propagates through them similar to a leaky-wave antenna as shown in Figure 2a. The simulated radiation pattern in Figure 2b shows a directional beam of gain about 19 dBi at 30 GHz with a maximum at 30° above the horizontal plane, showing the effective off-surface radiation.

As shown in Figures 2c,d, the reconfigurability of the surface-wave launcher enables the generation of diverse radiation patterns by strategically configuring the on-state cavities to form different launcher geometries. This capability is crucial for realizing advanced beamforming without any physical alteration of the hardware. For example, by arranging specific cavity patterns, the surface wave can be transformed into a single focused beam with a specific elevation angle or simultaneously divided into multiple distinct beams. These results demonstrate the potential dynamic control of the far-field radiation pattern and the proposed E-FAS functions not merely as a passive waveguide but as a reconfigurable radiating aperture. Furthermore, the well-established leaky-wave antenna theory will be employed to formulate the surface-wave propagation constant (β sw) of the surface wave in the launcher geometry, which provides a theoretical foundation for engineering various beam shapes and radiation angles in detailed investigations.

Figure 3 illustrates the simulation models of two operational scenarios for the E-FAS: the downlink, where signals propagate from the E-FAS to free space (in the form of a horn antenna), and the uplink, where signals travel from the free space (a horn antenna) to E-FAS. In the downlink scenario, a signal is received at the feeder, converted into surface wave on the E-FAS, guided along the SW channel to a desired position, and finally radiated into free space via the surface wave launcher. Conversely, in the uplink scenario, the launcher captures the wirelessly transmitted wave (a horn antenna is used to represent the source in the model), converts it into a surface wave, and guides it along the surface wave channel to the feeder. It can be observed that the downlink and uplink may not always be reciprocal. The downlink will transmit more energy to the free space, while in the case of uplink, as the surface wave launcher has finite footprint, it may not receive all the energy from the horn. To validate both scenarios, measurements were conducted with the E-FAS configured alternatively as the transmitter and as the receiver. The results will be presented in Section 3.

3 Results and discussion

To verify the performance of the proposed E-FAS, a prototype, which consists of a 20-cm-long surface wave channel integrated with a surface wave launcher, of total 25 cm (25 λ₀) long and 5 cm wide as shown in Figure 4a was fabricated and measured. The prototype and measurement setup are shown in Figure 4. During the measurement, EM waves radiated from the E-FAS are collimated by a reflector to produce a quasi-plane wave, which is then received by a standard-gain horn in a compact range antenna chamber. A laser positioning system was used to align the antennas and reflector.

Figure 5 shows the S₁₁ of the E-FAS. The interested operating frequency range is from 25.4 to 27.4 GHz. The bandwidth is mainly limited by the feeder design (Wan et al., 2019). shows a wideband feeder which can support 52 GHz of bandwidth. While the focus of this paper is to demonstrate the launch and reception of surface wave into/from free space, the detail of the feeder design is not included to keep the clarity. The measured radiation pattern of the single beam surface wave launcher is provided in Figure 6. Reasonably good agreement between the simulation and measurement is observed, the deviation in the radiation patterns is likely due to fabrication and assembly tolerances. Additionally, oscillations are visible outside the main beam direction, which are caused primarily by the phase interference. As illustrated in Figure 2a, interference arises from two sources: (i) direct radiation from the feeder into free space, and (ii) leakage of surface wave energy during propagation. The phase difference between these parasitic radiations and the main beam results in constructive and destructive interference, manifesting as the observed pattern oscillations.

Figure 6 shows the radiation pattern of the E-FAS in the downlink scenario, where the maximum realized gain is about 18.5 dBi at 26.4 GHz within the passband. The measured radiation patterns for both downlink and uplink are presented in Figure 7. In both cases, the E-FAS exhibits clear beam directionality. However, in the uplink case, the radiation level is approximately 2–4 dB lower over the frequency range of interest, which is attributed to the limited footprint of the launcher. As a result, the surface-wave launcher cannot capture all of the power radiated from the source.

These experimental results demonstrate that the Enormous Fluid Antenna System (E-FAS) effectively bridges the gap between guided wave propagation and reconfigurable radiation, providing a low-loss alternative to traditional over-the-air links. However, the transition from an experimental prototype to commercial 6G deployment presents several scalability challenges. One primary concern is the complexity of fabrication. The current E-FAS prototype relies on the precision machining of a porous surface with a high-density array of hollow cylindrical cavities spaced at 1.2 mm intervals. While CNC machining and manual metal-rod insertion are suitable for laboratory validation, large-scale implementation in practical systems would require more scalable manufacturing techniques. Advanced PCB fabrication processes, such as high-aspect-ratio laser drilling and automated surface-mount technology (SMT) for integrating switching elements like PIN diodes, will be necessary to maintain consistent electromagnetic performance across thousands of cavities.

A particularly promising path toward the high-volume production of the E-FAS involves leveraging the modular assembly method currently established for large-scale LED display panels. These systems share a fundamental geometric commonality: a massive planar aperture composed of discrete, repeating sub-wavelength units. By adopting a tiled modular architecture, individual E-FAS panels can be manufactured using standardized automated processes and subsequently interconnected to form an effectively enormous radiating surface. This modularity extends beyond physical construction to the electronic control layer. Much like the synchronization controllers used to coordinate pixel data across multiple LED cabinets, modular control units can be deployed to manage the switching states of the E-FAS cavities. These units ensure precise timing and phase synchronization between adjacent panels, which is a critical requirement for maintaining beamforming accuracy and aperture efficiency in massive wireless applications. This synergy with existing display manufacturing infrastructure could significantly reduce the barriers to commercial 6G deployment by utilizing mature supply chains for high-speed data distribution and power management across large physical areas.

From a cost perspective, the choice of materials and the density of the control circuitry are the main drivers of system expenditure. The use of high-performance dielectric substrates such as F4BM-2 is critical for maintaining a stable dielectric constant and low dissipation factor, yet the cost of such materials scales with the large apertures required for “enormous” antenna systems. However, E-FAS may offer a superior cost-to-performance ratio compared to conventional fully digital massive MIMO architectures by significantly reducing the number of active RF chains required. Additionally, a smaller number of shared RF sources will not incur significant phase noise as in MIMO, as reconfiguration is achieved through spatial switching of the radiating aperture rather than through independent phase-controlled active elements.

By using a single reconfigurable surface to perform both signal guiding and beamforming, the hardware complexity is shifted from expensive RF transceivers to lower-cost passive radiating elements and control logic. This approach aligns with findings in flexible intelligent metasurface (FIM) research, where 3D reconfigurability has been shown to reduce base station transmit power requirements by approximately 3 dB. The ultimate economic feasibility will depend on the development of low-power, integrated control modules (such as specialized ASICs) that can manage the switching states of thousands of elements with minimal power consumption and latency.

Integration strategies for commercial 6G networks must also address the significant overhead associated with channel state information (CSI) acquisition and real-time optimization. In systems with a massive number of reconfigurable elements, probing the two-hop channel becomes computationally expensive and introduces high signaling overhead. To mitigate this, E-FAS integration could involve a tiered control strategy where the surface wave “superhighways” are pre-configured for broad coverage areas, while the fine-grained cavity state optimization is performed dynamically for specific user locations. Jointly optimizing the transmit beamforming at the base station and the surface states of the E-FAS is essential for maximizing the signal-to-interference-plus-noise ratio (SINR) in multiuser environments. By combining the low-loss propagation of E-FAS with the spatial degrees of freedom provided by holographic MIMO and FIM technologies, future wireless systems can achieve the high data rates and energy efficiency required for the 6G era. To ensure the practical viability of the proposed surface-wave FAS (E-FAS) in the future 6G or beyond wireless systems, our research group is prioritizing the following key aspects: the impact of uplink/downlink differences on the system, scalability considerations, electronic control of the on/off states of the cavities, and, most importantly, the surface-wave launcher design in our research. We welcome other researchers to join us on this challenging journey.

4 Conclusion

This paper experimentally validates an enormous fluid antenna system (E-FAS) that unifies low-loss surface-wave signal guiding and reconfigurable high-gain radiation on a single porous platform. By selectively switching cavity states, the same structure realizes both efficient surface-wave channels and directive launchers, achieving a measured beam gain of about 18.5 dBi at 26.4 GHz with good agreement between simulation and experiment. These results confirm the feasibility of E-FAS as a programmable interface for future intelligent wireless systems. Future work will focus on electronic cavity reconfiguration, scalable modular implementation, and advanced leaky-wave-based beamforming and multi-point radiation to meet 6G and beyond connectivity and energy-efficiency demands.

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Footnotes

Edited by: Ghanshyam Singh, University of Johannesburg, South Africa

Reviewed by: Jiancheng An, University of Electronic Science and Technology of China, China

Ahmad Bazzi, New York University Abu Dhabi, United Arab Emirates