Tem Cell and GTEM Cells


What it means

The acronym 'GTEM' stands for GigaHertz Transverse Electromagnetic Mode, hence the GTEM Cell.
That is to say the TEM mode of propagation is dominant.  Detrimental higher modes can exist but are weak by virtue of the shape of the cell and the broadband resistor/absorber loading.  The GTEM Cell is in fact just the tapered feed section of the original parallel plate TEM cell - hence the addition of 'G' for GigaHertz.  The TEM Cell is severely limited in bandwidth by resonances (see below).

The GTEM Cell

The GTEM Cell enables users to perform radiated emissions and radiated immunity tests of small and medium-sized EUTs.

The advantages are a wide frequency range from 0 Hz up to 18 GHz, highly homogenous fields, good repeatability, high level of accuracy, low costs for installation and servicing, and others.

Benefits - GTEM Cell

  • Fulfils a Broad Range of Performance Requirements

  • Compact and Convenient

  • Permits EMC Testing in Less Time

  • Ready to Test When you are

  • Provides Accurate, Repeatable Results

  • Reliable Operation and Construction

History - Tem Cells

Small EUTs can be tested for RF susceptibility within a device known as a TEM cell. This consists of an enclosed transmission line of constant characteristic impedance Z0 within which a uniform field is developed (Figure 3). The EUT is placed between the plates in this field. The TEM cell's advantage is that because it is enclosed, high fields can be developed within it without the need for a surrounding screened enclosure, and so it can be used in the laboratory environment; also, it needs relatively little power to develop an adequate field strength.
Its disadvantage is limited frequency range, since over-moding of the transmission line and consequent variation of the field structure occurs above a cut-off frequency dependent on the cross-sectional dimensions.
The EUT should not occupy more than one-third of the space between the plates, and is not accessible for visual monitoring during the test. As an example, for an EUT height of 20cm the maximum frequency would be 200MHz.
For the history of the GTEM Cell see "Best Practice Guide" under "Library".