 |
|
 |
|
| Electromagnetic waves in various frequencies emitted by the sun cause noises that result in degradation of transmission signals. |
|
|
A directional beam antenna of a ground station
is always set to face a geostationary satellite. As the sun passes
the antenna beam's field of view, the ground station's receiver picks
up the sun interference that deteriorate the receive C/N; thus lower
quality of communications traffic. This phenomenon behaves as if the
noise temperature rises in the ground station's receiver. |
|
| Timing of sun interference occurrence can be geometrically
calculated by such factors as longitudinal position of a satellite,
latitude and longitude of a ground station, and a diameter of an antenna.
For ground stations on the north hemisphere, the sun interference
occurs for several days before the Spring Equinox and after the Autumnal
Equinox: vice versa on the south hemisphere. In case a ground station
is located west of a satellite, sun interference occurs in the morning.
And a ground station east of a satellite, sun interference in the
afternoon. |
|
 |
|
|
The angle of degrees B at which the sun crosses the
half power beamwidth of a receive antenna, where the half power beamwidth
of the antenna is Bo , is obtained as follows:
B = 0.5 + BoThe apparent diameter of the sun as seen
from the Earth is about 0.5 degree.
|
 |
|
For the sun rotates one degree in 4 minutes, the longest time length
the sun moves by the receive antenna's half power beamwidth, is calculated
as follows:
4 x B minutes
And for the sun's declination changes 0.4 degree a day, the maximum
number of days the sun stays within the receive antenna's half power
beamwidth is:
B / 0.4 days
A value of the receive antenna's half power beamwidth for typical
parabolic antennas, where wave length of receive frequency is L and
diameter of an antenna D, is predicted as follows:
Bo = 70 x L / D
Therefore, the larger diameter of a receive antenna is, the shorter
time and the fewer days sun interferences last.
Diameter of a receive antenna is related to quality of communications
traffic. As the antenna gain increases proportionally to diameter
of the antenna, the effects of sun outrages increase. How adverse
sun outrages can be determined not only by diameter of an antenna
but other factors like a signal margin of a ground station, noise
temperature of a receiver and communication systems.
|
|
|
