ETTC'2003 - SEE

2.2 Limitation of conventional Gain flatness Measurement method
IOT gain flatness measurements are historically performed using a continuous
sweep of the bandwidth without controlling the variation of the reference point.
This method doesn’t take into account the variations of the measurements
conditions such as temperature of the RF chain, antennas gain slope combined
with satellite motion, propagation through the atmosphere fluctuations.
The Figure 1 and Figure 2 are representative of obtained previous IOT
measurements done on several satellites: all tests results are tilted leftward.
The Figure 3 present a comparison between the ground test result during
ambient phase (Reference test) and the result obtain during IOT (In Orbit Test)
phase.
Relative Level (dB)
Comparative result AIT ambient / IOT conventional method
1
0,5
0
-2 -1,5 -1 -0,5 0 0,5 1 1,5 2
-0,5
-1
-1,5
-2
Freq offset (MHz)
-4-
Relative level ambient result
relative level IOT
Figure 3 comparative result ambient ground test with In Orbit Test conventional
method