  The Square Kilometre Array (SKA) project is an international effort to build
the world's most sensitive radio telescope operating in the 50 MHz to 14 GHz
frequency range. Construction of the SKA is divided into phases, with the first
phase (SKA1) accounting for the first 10% of the telescope's receiving
capacity. During SKA1, a Low-Frequency Aperture Array (LFAA) comprising over a
hundred thousand individual dipole antenna elements will be constructed in
Western Australia (SKA1-LOW), while an array of 197 parabolic-receptor
antennas, incorporating the 64 receptors of MeerKAT, will be constructed in
South Africa (SKA1-MID).
  Radio telescope arrays, such as the SKA, require phase-coherent reference
signals to be transmitted to each antenna site in the array. In the case of the
SKA, these reference signals are generated at a central site and transmitted to
the antenna sites via fibre-optic cables up to 175 km in length. Environmental
perturbations affect the optical path length of the fibre and act to degrade
the phase stability of the reference signals received at the antennas, which
has the ultimate effect of reducing the fidelity and dynamic range of the data
. Given the combination of long fibre distances and relatively high frequencies
of the transmitted reference signals, the SKA needs to employ
actively-stabilised frequency transfer technologies to suppress the fibre-optic
link noise in order to maintain phase-coherence across the array.
