ETS-Lindgren 5411 GTEM! Test Cell - Manual (Page 46)

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GTEM! Use
Software Computations
The correlation algorithm software for the GTEM! performs the calculations as
outlined in the following.
At each frequency, the three-position correlation algorithm:
 Performs a root sum of the squares summation of the
three orthogonal voltages.
 Computes the total power emitted by the EUT as determined from
the summation of the three voltages and the transverse
electromagnetic mode (TEM) mode equations for the GTEM!.
 Computes the current excitation of an equivalent tuned, half-wave
Hertizian dipole when excited with that input power.
 Computes the field intensity at appropriate height intervals over the
total, operator selected scan height, either one to four meters or
two to six meters for both vertical and horizontal polarizations of the
receive antenna when the equivalent turned resonant dipole is
placed at an appropriate height over a perfect ground plane.
 Selects the maximum field strength (larger) value of the horizontal or
vertical polarizations.
 Presents this maximum value for comparison to the chosen
EMC specification limit.
The GTEM! feed connector voltages produced by radiated emissions from the
EUT at each of three orthogonal axes are measured, then at each frequency an
equivalent set of fixed dipole antennas that would produce the same voltages at
the GTEM! connector are defined through computer computation. Once these
equivalent antennas are defined, the OATS field intensities are computed for the
distances and height scans selected. The calculated OATS data is then
presented for comparison to actual OATS data if available based on an OATS
emission limit.
The accuracy of the measurement is of prime importance. A report on the relative
accuracy of the GTEM! for radiated emissions measurements is provided in
Appendix C, Radiated Emissions Test Performance on page 71.