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7.4.2 SATTANT
SATTANT is the name AvL has assigned to a novel approach developed to refine the antenna base
heading provided by the electronic compass using satellite received signal power, only. Unlike
methods employed by other antenna controllers to refine the compass heading, SATTANT does not
require a DVB receiver or an extensive, up-to-date satellite location database. A simple and
inexpensive broadband power detector (RSL) is all that is required. This method provides an
accurate estimate of antenna heading immediately out-of-the-box anywhere the antenna system is
deployed.
This approach depends only on accurate knowledge of the antenna’s location and the elevation
angle of the antenna’s bore-sight. The GPS antenna and receiver included in every AvL antenna
system provides location information to accuracy much higher than the SATTANT process needs. A
carefully calibrated elevation inclinometer provides an accurate estimate of the antenna’s elevation
angle relative to the local gravity vector.
Based on the antenna’s location and heading, the imaginary line in the sky traced by the
geostationary satellite arc can be calculated. The two points at which a line of constant elevation
angle intersects that geostationary satellite arc can also be calculated with precision and expressed
in terms of elevation angle and azimuth angle relative to true North. These intersecting lines are
illustrated in Figure 7.4.2. Successfully acquiring and peaking on any geostationary satellite provides
the information (pedestal elevation and azimuth angles) necessary to substantially improve the
antenna heading estimate and allow the antenna to zero in on the target satellite’s location.
