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The RF power amplifier fades up the low output signal of the RF generator. Now, the RF signal
is powerful enough to feed the antenna and generate a high-intensity RF field. Depending on the measuring space and the desired field strength there is an amplifier power needed reaching from a few Watts up to several 10 kW. In general, the gain of an amplifier is subjected to a drift. There are various reasons for it, eg aging, operating time, ambient temperature, mains voltage, etc.. To compensate those effects this EMC test set-up provides a gain control (via directional coupler and power meter). |
Of course, if an high-quality amplifier is used the manufacturer has taken constructive measures to reduce
this drift to a negligible degree. This means, it is also possible to do EMC testing without any gain control. That method is much faster than controlling the output power, since there is no additional time needed to level the output power at every frequency step. |