  Fluid antenna systems (FAS) are an emerging technology that promises a
significant diversity gain even in the smallest spaces. Motivated by the
groundbreaking potentials of liquid antennas, researchers in the wireless
communication community are investigating a novel antenna system where a single
antenna can freely switch positions along a small linear space to pick the
strongest received signal. However, the FAS positions do not necessarily follow
the ever-existing rule separating them by at least half the radiation
wavelength. Previous work in the literature parameterized the channels of the
FAS ports simply enough to provide a single-integral expression of the
probability of outage and various insights on the achievable performance.
Nevertheless, this channel model may not accurately capture the correlation
between the ports, given by Jake's model. This work builds on the
state-of-the-art and accurately approximates the FAS channel while maintaining
analytical tractability. The approximation is performed in two stages. The
first stage approximation considerably reduces the number of multi-fold
integrals in the probability of outage expression, while the second stage
approximation provides a single integral representation of the FAS probability
of outage. Further, the performance of such innovative technology is
investigated under a less-idealized correlation model. Numerical results
validate our approximations of the FAS channel model and demonstrate a limited
performance gain under realistic assumptions. Further, our work opens the door
for future research to investigate scenarios in which the FAS provides a
performance gain compared to the current multiple antennas solutions.
