Considerations about the use of the Moon in X-band antenna G/T measurements

Darko Šekuljica, Stefano Badessi, Massimiliano Ferrante, Matjaž Vidmar


The most common G/T quality factor measurement methods applicable for operational X-band parabolic antennas with a reflector aperture diameter between 7 and 13m have been reviewed. Analysis have shown that the most adequate RF source for the G/T measurement of the antennas of interest is the Moon.

Since Moon’s angular diameter is wider than the antenna’s Half Power Beam Width (HPBW), a thorough analysis of the extended source size correction factor was performed. As a result, an efficient correction factor approximation method which is more accurate in case of efficiency losses was identified, and a best-fit estimation method for the HPBW verification has been introduced.

The proposed G/T quality factor measurement procedure has been verified on an operational X-band 11 meter Cassegrain antenna, used for Low Earth Orbit (LEO) satellite data acquisition. The results obtained with the proposed method, have provided accurate G/T factor estimations that are consistent and in line with the expectations. As further confirmation, the validity of the measurement method results was also verified against a G/T measurement done with the Cassiopeia A radio star as an RF source.


X-band; G/T measurements; Moon; Satellite communications; Extended source size correction factor

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