ETS-Lindgren 5411 GTEM! Test Cell - Manual (Page 40)

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GTEM! Use
Radiated Emissions Measurements – Hardware Requirement
Measurement of radiated emissions requires the use of a frequency-selective
EMI meter or spectrum analyzer. For manual use, any calibrated receiver
typically used for electromagnetic compatibility (EMC) measurements is
acceptable as long as the test specification requirements for the measurement
device are met.
EUT Orientation for Testing
Proper orientation of the EUT in three orthogonal axes is necessary to accurately
perform radiated emissions measurements. To perform the EUT rotations,
separate coordinate axes are defined for the GTEM! and the EUT. The
mathematical model for the correlation to an OATS and the need for the
three orthogonal rotations is described in Appendix B, Emission Measurements
in TEM Cells and TEM Lines on page 69.
The three reference orthogonal axes of the GTEM! are normally defined as:
 Positive Z-axis: to the feed
 Positive Y-axis: up
 Positive X-axis: toward the right of the cell as seen from the apex
Note that this is a positive right rectangular coordinate system; X rotated into Y in
a right-handed sense gives a positive-Z. In this discussion the uppercase letters
X, Y, and Z represent the axes of the GTEM! , and the lowercase letters x, y,
and z represent the EUT right axes.
The mathematical formulation of the GTEM! model for determining the
OATS-equivalent value of radiated emissions requires three measurements of
voltage produced by the EUT in three orthogonal axes positions. In the rotation
scheme, the three positions must be aligned with the axes of the cell as follows:
Position 1: GTEM! axes XYZ
EUT axes xyz
Position 2: GTEM! axes XYZ
EUT axes yzx
Position 3: GTEM! axes XYZ
EUT axes zxy