cell is a TEM waveguide with the upper frequency limit extended to
the GHz range. It is a low-cost alternative measurement facility for
both radiated emission and immunity measurements. It is included in
the published standard IEC 61000-4-20 “Emission and
Immunity Testing in Transverse Electromagnetic (TEM) Waveguides”.
Compared to other measuring methods like EMC test in anechoic
chambers or OATS (Open Area Test Sites), GTEM Cells offer some
significant advantages for the testing of small and medium sized
EUT´s (Equipment Under Test) up to a frequency range of 20GHz. Quick
turnarounds of the EUT as well as numerous testing variations are
easy and fast to
handle. Switching from emission to immunity testing requires only
simple adjustments, from receiver input to amplifier output.
irrespective of long waiting times associated with off-site test
labs or weather and ambient delays that can occur at OATS
facilities. Whether you are at the design qualification,
pre-compliance, compliance, or production sampling stage, the GTEM
is the right choice for you.
GTEM Cells acc.
to IEC/EN 61000-4-20
GTEM test set-up for radiated immunity tests
and emission measurements
Connection to the loop is through a BNC connector which enables
coaxial cabling to the EMI receiver. The loop is supplied with a
correction factor graph showing the values in dB which must be added
to the reading of a 50 ohm EMI meter to obtain answers in either dB/μV/m
or dB/pT. The correction factor decreases as frequency increases
from 30 Hz up to approximately 15 KHz, where the factor levels off
and remains relatively constant up to 5 MHz.
The Type 7334-1 Loop Antenna is required by Test Method RE01 in
Parts 2 through 6 of MIL-STD-461C and RE101 of MIL-STD-461D.These
portions of the specification require magnetic field emission tests
of cables, equipments, systems and sub-systems installed in, or used
in, all phases of military vehicles, ships, submarines, aircraft
(including helicopters), spacecraft, or ground-based operations.
TEST METHODS RE01 and RE101
The Type 7334-1 Loop Antenna is positioned 7 cm from the face of the
equipment under test with the plane of the loop parallel to the
equipment face. The best position to begin with is opposite or near
a joint or seam.
The associated EMI meter is then scanned over the range 30 Hz to 100
KHz searching for emissions. At the frequencies where emissions are
found, the loop antenna is moved about the surface seeking the
strongest emission level.
When a strong signal is detected, the loop is oriented on its axis
for a maximum reading. This procedure is repeated for all surfaces
of the equipment under test. Although the specification is not clear
on the point, it appears to indicate that all six sides (including
the bottom) of an equipment must be tested in this manner.
When testing cables, the loop antenna is placed 7 cm from the cable
with the plane of the loop parallel to the cable. The non-metallic
base plate of the Type 7334-1 Loop Antenna provides a convenient
means for establishing the correct 7 cm distance.