Design and Experimental Validation of mmWave Surface-Wave-Enabled Fluid Antennas for Future Wireless Communications

While multiple-input-multiple-output technologies continue to advance, scalability challenges persist. The fluid antenna system (FAS) offers position flexibility, significantly reducing its dependence on channel-state-information spatial adaptation with only a single RF chain. However, most existing FAS studies remain theoretical and lack experimental validation. This letter presents two fully implemented fluid-antenna prototypes featuring dynamically position-flexible radiators. Enabled by surface-wave launchers, 3-D-printed fluidic channels, and a fluid-control system, a single-channel and a double-channel fluid antenna are simulated, fabricated, and measured. The measured S11 confirms operation within the 24 GHz to 30 GHz 5G millimeter-wave (mmWave) band, and the radiation patterns exhibit spatial variations as the radiator position changes. Crucially, the novelty of this work does not lie in improving traditional antenna parameters, such as gain or isolation; rather, it introduces a new communication mechanism in which position-flexible radiation reshapes the wireless channel to escape deep fading - something fixed antennas fundamentally cannot achieve. The results demonstrate that compact fluid-antenna designs provide a practical solution for future mmWave systems requiring reconfigurability and spatial adaptability.