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EMI Pre-Compliance Guide RIGOL Technologies
RIGOL Technologies CO., LTD. 09.09.2021
In most cases such kind of test chamber is not available for pre-compliance analysis.
Therefore alternative ways has to be evaluated.
First of all, it is possible perform a free field measurement with the distance of radiated near
field which is defined for 0.159 * λ to 4 * λ. In this region a far field evaluation is possible (with
using correction values). To detect the test area attenuation
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from environment it is possible
to perform a test with a counter antenna instead of DUT and the results will be compared
with defined formula of theoretical value. The difference is the test area attenuation.
Depending on the distance between antennas, variable correction factors are used. This test
needs a very good conductive ellipsis area
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. There shall be no conductive obstacles greater
than 5 cm within the ellipsis (see figure 12). DUT and test antenna are located within the
focus of ellipsis. It is necessary to perform an altitude variation of test antenna to detect
maximum.
This test is very time intensive and expensive. A more simple way of radiated emission
analysis for pre-compliance test is, to use a TEM cell.
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It could happen that obstacles outside the ellipsis occurs unwanted reflections. Therefore the test area
attenuation needs to be evaluated, first.
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This could be realized with metal foil or with a wire mesh area
Figure 12: free field measurement for radiated emission
Figure 13: Double port TEM cell