GTEM cell: what it is 

What is a GTEM cell

A GTEM cell is a widely used instrument for generating known, homogeneous fields in the laboratory. In particular, it is easy to emulate the electric and magnetic fields characteristic of a plane wave over a wide frequency band, ensuring good field uniformity in the operating region. Because of these characteristics, TEM/GTEM cells are frequently used for the calibration of precision instruments for measuring electric and magnetic fields, as well as for Electromagnetic Compatibility (EMC) studies. It is a key instrument for the calibration of electric and magnetic field measuring instruments and for Electromagnetic Compatibility (EMC) studies, as it is able to simulate the effects of an incident plane wave (TEM mode) over a wide frequency band, ensuring field uniformity in the operating region. A TEM cell is a transmission line in which the fundamental propagative mode is TEM, having a particular shape that makes it suitable for housing within it, in an area where the fields are homogeneous, devices on which laboratory tests can be performed. 

How it is composed 

A GTEM cell consists of a power connector into which the radio frequency signal is injected. This is followed by a transmission line that is progressively expanded, resulting in the typical pyramid shape. The impedance of the line is kept constant, leaving the proportions of the conductors unchanged. After a possible central section with constant cross-section, there follows a further progressive reduction in cross-section, symmetrical to the first. The resulting transmission line is finally terminated on a resistive load equal to the line impedance, in order to avoid standing waves. In order to reduce the length of the device, which can reach several metres, it is possible to truncate the structure and introduce a broadband termination. In this way, the so-called GTEM cell is obtained.

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