The TEM cell offers a broadband method of measuring either immunity of a DUT to fields generated within the cell or radiated emissions from a DUT placed within the cell. It eliminates the use of conventional antennas with their inherent measurement limitations of bandwidth, non-linear phase, directivity and polarization. The TEM cell is an expanded transmission line that propagates a TEM wave from an external or internal source. This wave is characterized by orthogonal electric (E) and magnetic (H) fields that are perpendicular to the direction of propagation along the length of the cell or transmission line. This field simulates a planar field generated in free space with an impedance of 377 ohms. The TEM mode has no low frequency cutoff. This allows the cell to be used at frequencies as low as desired. The TEM mode also has linear phase and constant amplitude response as a function of frequency. This makes it possible to use the cell to generate or detect a known field intensity. The upper useful frequency for a cell is limited by distortion of the test signal caused by resonances and multi-moding that occur within the cell. These effects are a function of the physical size and shape of the cell.
The 1 GHz TEM cell is of a size and shape, with impedance matching at the input and output feed points of the cell, that limits the VSWR to less than 1.5:1 up to its rated frequency. It is tapered at each end to adapt to conventional 50 ohm coaxial connectors and is equipped with an access port to accommodate the standardized IC test board. The first resonance is demonstrated by a high VSWR over a narrow frequency range. The high Q of the cell is responsible for this high VSWR. A cell verified for field generation to a maximum frequency will also be suitable for emission measurements to this frequency.
AE J1752-3 Measurement of Radiated Emissions from Integrated Circuits – TEM / Wideband TEM (GTEM) Cell Method, TEM Cell (150 kHz to 1 GHz), Wideband TEM Cell (150 kHz to 8 GHz) Society of Automotive Engineers, 400 Commonwealth Drive, Warrendale, PA 15096-0001, USA, (412) 776-4841.
IEC 61967-2: Integrated circuits - Measurement of electromagnetic emissions, 150 kHz to 1 GHz - Part 2: Measurement of radiated emissions, TEM Cell and wideband TEM cell method.