ETS-Lindgren 5411 GTEM! Test Cell - Manual (Page 75)

Radiated Emissions Test Performance of GTEM!
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R
EFERENCE
D
IPOLE
A
NTENNA
T
ESTING
Equivalence testing for GTEM! was planned using tunable dipole antennas. The
tunable antennas can remain comparatively small over the majority of the
frequency range of interest, and dipole antennas are the reference antennas
constructed as described in ASNI 63.5, preferred for the resolution of conflicting
measurements. The dipoles can be easily placed in the center of the test volume
and three orthogonal measurements made to satisfy the requirements for
GTEM! testing. They are also easily transferred to the OATS for the comparison
testing. When the dipole antennas begin to become large with respect to the size
of the GTEM! test volume, they were used as short dipoles with the dipole
elements set to a fixed frequency compatible with the size of the test volume.
The resonant dipoles were installed on an OATS with the feed point of the dipole
directly over the center of the turntable. The dipole was driven at many
frequencies, as appropriate, to 1000 MHz. The test procedure of ANSI 63.4, was
used. This procedure requires that the measurement be made at the maximum of
the emanation at each frequency. This in turn requires searching the receive
antenna in height, and rotation of the turntable to establish the maximum value of
the emanation. Measured values were corrected to field strength values by
adding cable loss and antenna factors.
The resonant dipoles were then transferred to the test volume of the GTEM!.
Voltage measurements were made in three orthogonal orientations, and test
control software was used to process the three orthogonal measurements into
field strength versus frequency data. These values are directly comparable to
those taken at the OATS.