ETS-Lindgren 5411 GTEM! Test Cell - Manual (Page 61)

Manual EUT Manipulator Operation Theory
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S
PECIAL
M
EASUREMENTS
Special measurements are sometimes required because the EUT may have
gain greater than a dipole, in which case the radiation pattern may be cardioid or
other unidirectional pattern. Above about 500 MHz, some EUT may have an
incidental unidirectional pattern because of the way they are constructed, but
others have a unidirectional pattern because they are intentional transmitters with
a built-in antenna. Two algorithms may be used depending on what one wants to
know about the EUT. The simplest one is the 12-measurement, sorted
three-input correlation algorithm, and the other one is the 12+4-position
correlation algorithm, In both of these algorithms, the EUT is viewed as a cube
and measurements are taken of the emission from each face in both
polarizations. The 12-measurement, sorted three-input correlation is used when it
is not necessary to know anything about the shape of the radiation pattern of
the EUT. It is often used to test small telecom terminal equipment, such as
cellular telephones, up to 10 GHz. It is valid from 30 MHz to at least 10 GHz. The
12+4-postion correlation algorithm is used to estimate the shape of the radiation
pattern of the EUT. It is valid from 30 MHz to 5 GHz.
I
MMUNITY
M
EASUREMENTS
Immunity measurements may be made in the GTEM! to satisfy standards such
as MIL-STD-462 or IEC 61000-4-20. If the shape of the radiation (sensitivity)
pattern of the EUT is unknown, then the front, back, and both sides must all be
exposed to the test signal in both horizontal and vertical polarizations. To do this,
eight positions must be tested so that the four usually vertical sides of the EUT
are tested in both polarizations facing the apex of the GTEM!. If the operator
already knows that only one side (for example, the back) of the EUT is sensitive
to external electromagnetic fields, then the testing can be reduced to exposing
only the one sensitive side to the apex of the GTEM! in both polarizations.
Installing the Manipulator and EUT
Position the cradle turntable, base turntable, and cradle tilt to the 0-degree
marks. For the Model 5407, place the manipulator such that the grooves straddle
the center seam strip. The suggested start position is with the cradle side plates
perpendicular to the center longitudinal seam, and spaced approximately 20 cm
from the absorber tips. Place the EUT on the cradle turntable and secure it with
non-metallic cords or rope. Polystyrene blocks may be placed under the EUT for
elevation before securing. For the Model 5411, place the manipulator so that the
unit is positioned approximately 20 cm from the absorber tips. Center the
manipulator along the longitudinal axis of the GTEM!. Rubber feet will help
maintain the position during testing.