ETTC'2003 - SEE

3.2 Analysis of the contribution
There is a general trend for all these measurement; there is an additional gain
slope.
The elapsed time of this measurement is 20 minutes, for 44 points of
measurement.
Perturbations could have several origins:
- Propagation: variations of propagation conditions in the atmosphere may
change during the measurement duration. The higher the frequency, the
larger the contribution.
- Motion of the satellite combined with antennas gain slope : this results in
a modification of the payload antenna pointing to the ground station
direction. Its effect depends on the location of the IOT station within the
Satellite antenna diagrams.
- Ground station stability: thermal RF ground chain stability, antennapointing
stability, and measurement equipment stability…
- Satellite temperature: RF gain chain during the elapsed time
The previous In Orbit Tests have all presented a dispersion of 0.25 dB to 0,5 dB
for 3 MHz until 30 MHz bandwidth filter.
3.3 Advantage of the new IOT Gain flatness Measurement method
This new method allows to compensate all these medium-term drifts affecting
the measurement conditions.
Realtive Level (dB)
Comparison of ambient result and proposed IOT method
1
0,5
0
-2 -1,5 -1 -0,5 0 0,5 1 1,5 2
-0,5
-1
-1,5
-2
Frequency Offset (MHz)
-9-
New method
Ambient result
Figure 9 Comparison of ambient ground test result with IOT proposed method