  While multiple-input multiple-output (MIMO) technologies continue to advance,
concerns arise as to how MIMO can remain scalable if more users are to be
accommodated with an increasing number of antennas at the base station (BS) in
the upcoming sixth generation (6G). Recently, the concept of fluid antenna
system (FAS) has emerged, which promotes position flexibility to enable
transmitter channel state information (CSI) free spatial multiple access on one
radio frequency (RF) chain. On the theoretical side, the fluid antenna multiple
access (FAMA) approach offers a scalable alternative to massive MIMO spatial
multiplexing. However, FAMA lacks experimental validation and the hardware
implementation of FAS remains a mysterious approach. The aim of this paper is
to provide a novel hardware design for FAS and evaluate the performance of FAMA
using experimental data. Our FAS design is based on a dynamically
reconfigurable "fluid" radiator which is capable of adjusting its position
within a predefined space. One single-channel fluid antenna (SCFA) and one
double-channel fluid antenna (DCFA) are designed, electromagnetically
simulated, fabricated, and measured. The measured radiation patterns of
prototypes are imported into channel and network models for evaluating their
performance in FAMA. The experimental results demonstrate that in the 5G
millimeter-wave (mmWave) bands (24-30 GHz), the FAS prototypes can vary their
gain up to an averaged value of 11 dBi. In the case of 4-user FAMA, the
double-channel FAS can significantly reduce outage probability by 57% and
increases the multiplexing gain to 2.27 when compared to a static
omnidirectional antenna.
