GTEM cell

A GTEM or gigahertz transverse electromagnetic cell is a type of electromagnetic compatibility (EMC) test chamber used for radiated EMC testing.
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 tests correlated at "Far-field" conditions according to the requirements of the standard EN 61000-4-20. A GTEM cell provides homogeneous electromagnetic fields with TEM (Transverse electromagnetic wave mode) distribution, similar to the free space. The electric and magnetic field inside the cell can be accurately predicted using numerical methods. A GTEM cell external 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. Basically, the GTEM cell is a tapered rectangular 50 Ohm transmission stripline closed on a 50 Ohm load where the inner is called SEPTUM. The GTEM cell begins with a precision CNC craft transition: APEX, where a standard 50 Ohm coaxial connector (7/16", N, or SMA type) to the asymmetric rectangular waveguide is done. The GTEM is terminated on a lined surface made of
radiation-absorbent material (RAM) such as carbon foam loaded; metal oxides multilayers hybrid absorbers with ferrite tiles with the side walls able to act as a waveguide. A slightly spherical wave propagates from the APEX source to the loaded tapered waveguide, since the solid opening angle is small, the undistorted spherical wave can be considered as a plane wave. To minimize phase delays that may occur in big GTEM, the termination surface of the absorbers is shaped as a spherical sector. The termination load section uses absorbing material for an electromagnetic wave and a distributed resistive load for current termination. At low frequencies, it operates as a circuit 50 Ohm load; at high frequencies, the absorbers attenuate the incident waves as in an anechoic chamber, In this way, a termination from DC to several Gigahertz is achieved. 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:
The main goals of the GTEM against Semi- and full anechoic chambers are:
Principles of operation.
The GTEM cell forms an enclosed TEM (transverse electromagnetic mode) stripline, which acts as receiving emissions or transmitting emissions antenna: