A GTEM or Gigahertz Transverse Electromagnetic cell is a type of electromagnetic compatibility (EMC) test chamber intended for radiated immunity (susceptibility) and emissions testing. EMC test chambers allow for the performance of fast and efficient EMC radiated tests at a convenient location, without interference from the ambient electromagnetic environment.
In a GTEM cell, the conductive metal outer enclosure is in the shape of a long, rectangular pyramid. The pyramid is normally laid flat on one side, although occasionally it may be stood on its base. The base is typically covered internally with radiation absorbent material (RAM) but the side walls are left bare to act as a waveguide. An RF antenna is placed internally near the base, and a resistive RF absorber or load at the apex. In operation the equipment under test is placed in between the antenna and the load.
The GTEM cell provides a special form of enclosed TEM (transverse electromagnetic mode) stripline, which acts as receiving emissions or transmitting emissions antenna:
- When measuring Radiated Emission - one end of the stripline is connected to a Spectrum analyzer. The other end is terminated with RF load(50Ω).
- When measuring Radiated Immunity - one end of the stripline is connected to a source of radiation (Signal generator). The other end is terminated with RF load.
In operation, emitted radiation (whether from an antenna or from the EUT), 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.
- Nothofer, A, Alexander, M J, Bozec, D, Marvin, A and McCormack, L; Measurement Good Practice Guide No. 65: The use of GTEM cells for EMC measurements, National Physics laboratory, 2003. ISSN 1368-6550.
- using gtem cells for immunity testing - Evaluation Engineering