  The realization of photonic microwave oscillators using optomechanical
cavities has recently become a reality. By pumping the cavity with a
blue-detuned laser, the so-called phonon lasing regime - in which a mechanical
resonance is amplified beyond losses - can be reached and the input signal gets
modulated by highly-coherent tones at integer multiples of the mechanical
resonance. \textcolor{Red}{Implementing optomechanical cavities on released
films with high index of refraction can lead to optical modes at telecom
wavelengths and mechanical resonances in the GHz scale, resulting in
highly-stable signals in the microwave domain upon photodetection}. Owing to
the extreme compactness of such cavities, application in satellite
communications (SATCOM) seems highly appropriate, but no experiments have been
reported so far. In this paper, an optomechanical microwave oscillator (OMO)
built on a micron-scale silicon optomechanical crystal cavity is characterized
and tested in a real SATCOM testbed. Using a blue-detuned laser, the OMO is
driven into a phonon lasing state where multiple harmonics are generated,
reaching tones up to 20 GHz. Under this regime, its practical applicability,
remarkably addressing its performance as a photonic local oscillator, has been
validated. The results, in addition with the advantages of extreme compactness
and silicon-technology compatibility, make OMOs very promising candidates to
build \textcolor{Red}{ultra-low} weight photonics-based microwave oscillators
for SATCOM applications.
