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The apparent motion of an inclined orbit satellite appears as a narrow figure 8 pattern aligned
perpendicular to the geo-stationary satellite arc. As the inclination of the satellite increases both
the height and the width of the figure 8 pattern increase. The single axis tracker can follow the
long dimension of the figure 8 but cannot compensate for the width of the figure 8 pattern. A
paper (available on our web site - http://www.researchconcepts.com/Files/track_wp.pdf)
sufficient to accommodate the greatest satellite inclination that will be encountered.
Many people feel that single axis tracking is viable for antenna's up to 3.8 meters at C band and
2.4 meters at Ku band. Implicit in this is the fact that the inclination of most commercial
satellites is not allowed to exceed 5 degrees. This assumption should be verified before a system
is fielded.
A single axis tracking system must be in precise mechanical alignment to minimize loss due to
the mount's inability to compensate for the width of the figure eight pattern. For this reason, a
single axis tracker is more difficult to setup than other inclined orbit satellite tracking mounts.
Conversely, the operation of a single axis tracking antenna is more straightforward than that of
dual axis antennas. The satellite will always be located somewhere within the antenna's range of
travel so there is no danger of peaking up on an adjacent satellite. The controller can be operated
with the search feature enabled – even for transmit applications.
Control Axis Tilt for a Single Axis Tracking Satellite Antenna
The control axis of the antenna should be rotated by an amount equal to...
-ATAN[ sin(delt_L) / tan(L) ]
where L is the earth station latitude and delt_L is the difference in longitude between the satellite
and the antenna. The sense of the angle is relative to an observer located behind the antenna
looking through the antenna at the satellite. Positive angles correspond to a clockwise deflection
from vertical, negative angles correspond to a counter-clockwise deflection from vertical. This
Single Axis Tracking with the RC1500B
describes the height and width of the figure 8
pattern as a function of the inclination of the
satellite's orbit.
Note that the inclination of the satellite
increases with time. The maximum rate of
increase is approximately 0.9 degrees per
year. As the inclination increases, the width
of the figure 8 pattern will also increase. This
has two implications for system performance.
One, the maximum signal loss due to antenna
misalignment will increase with time, and
two, the antenna must have range a of motion
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