GTEM cell

A GTEM or gigahertz transverse electromagnetic cell is a type of electromagnetic compatibility (EMC) test chamber used for radiated EMC testing.[1]

Description

The GTEM is an alternative EMC site (than SAC = Semi-anechoic chamber, FAC = fully anechoic chamber or OATS = Open Area Test Site) to perform emission and immunity test in "Far-field" conditions according to the requirements of the EMC measurements. A GTEM cell enclosure is made of conductive material such as metal, in the shape of a long, rectangular base pyramid. The pyramid is normally laid flat on the major side (bottom), although occasionally it may be stood on its base.

The base is typically lined internally with radiation-absorbent material (RAM) such as carbon foam loaded; hybrid absorbers with ferrite tiles, but the side walls are left bare to act as a waveguide. A stripline tapered conductor, known as the septum, connects internally the input/output port apex connector and a hybrid termination resistive and RAM absorbers. Under test operation, the D.U.T. (Device under test) is placed in the test volume in between the septum and the bottom chassis. Usually, the test volume size is considered as one cube of 1/3 up to 1/2 height of the septum to the bottom distance: Within the test volume, the TEM (Transverse Electromagnetic) field is considered uniform within an uncertainty of +/- 3dB or +/-5dB. Theoretically, the GTEM is a broadband device able to operate from DC to Microwaves with some restrictions and compromises that conditioning the applications such as surface resistivity of the conductive metal adopted; quality of the RAM, Distortion and not TEM mode that could appear increasing the frequency.

Principles of operation

The GTEM cell forms an enclosed TEM (transverse electromagnetic mode) stripline, which acts as receiving emissions or transmitting emissions antenna:

  • When measuring radiated emissions, one end of the stripline is connected to a spectrum analyzer. The other end is terminated with an RF load (e.g., 50Ω).
  • When performing radiated immunity, one end of the stripline is connected to a source of radiation (signal generator). The other end is terminated with an RF load.

In operation, emitted radiation (whether from an antenna or from the equipment under test) travels along the length of the chamber and is absorbed by the absorbent load at the end.

For immunity tests, the field uniformity and the crosspolar coupling of the cell have to be within certain limits set by IEC 61000-4-20.[2]

References
  1. "GTEM". eevblog.com. Retrieved 2011-09-22.
  2. "York EMC, GTEM practice guide" (PDF). Retrieved 2013-01-18.

Notes

Datasheet of GTEM 1500 by GTEMCELL with a movie inside Datasheet of GTEM 2600 made by GTEMCELL Datasheet of the best high-quality military GTEM 1000 INOX engineered and made in Italy

Bibliography
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