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ETTC'2003 - SEE

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2.2 Limitation of conventional Gain flatness Measurement method<br />

IOT gain flatness measurements are historically performed using a continuous<br />

sweep of the bandwidth without controlling the variation of the reference point.<br />

This method doesn’t take into account the variations of the measurements<br />

conditions such as temperature of the RF chain, antennas gain slope combined<br />

with satellite motion, propagation through the atmosphere fluctuations.<br />

The Figure 1 and Figure 2 are representative of obtained previous IOT<br />

measurements done on several satellites: all tests results are tilted leftward.<br />

The Figure 3 present a comparison between the ground test result during<br />

ambient phase (Reference test) and the result obtain during IOT (In Orbit Test)<br />

phase.<br />

Relative Level (dB)<br />

Comparative result AIT ambient / IOT conventional method<br />

1<br />

0,5<br />

0<br />

-2 -1,5 -1 -0,5 0 0,5 1 1,5 2<br />

-0,5<br />

-1<br />

-1,5<br />

-2<br />

Freq offset (MHz)<br />

-4-<br />

Relative level ambient result<br />

relative level IOT<br />

Figure 3 comparative result ambient ground test with In Orbit Test conventional<br />

method

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