Field Chamber
Transverse electromagnetic transmission structures forming closed, rectangular co-axial testing environments generate uniform electromagnetic fields for high-frequency component evaluation. Engineers use a TEM cell to measure radiated emissions and RF immunity of small printed circuit assemblies without requiring full-scale anechoic chambers. Applicable frequency limits for a TEM cell stop where higher-order cavity resonance modes develop, typically restricting accurate measurements to frequencies below one gigahertz.
Immunity Measurement
A TEM cell consists of a rectangular outer conductor housing a flat central septum that acts as the inner conductor, connected to 50-ohm RF ports at both tapered ends. Placing a test circuit board between the septum and outer wall exposes the assembly to a controlled transverse electromagnetic field with uniform wave impedance equal to free space. RF signal generators connected to the cell inject high-level fields to test immunity, while spectrum analyzers detect radiated energy emitted by operating circuit boards.
Compact dimensions and shielded construction eliminate ambient electromagnetic interference from background measurements. Proper orientation of the test board inside the cell is critical, as field coupling depends on the orientation of PCB traces relative to the internal electromagnetic wave.
Radiation Mapping
Comparative testing using TEM cells provides rapid pass and fail feedback during early hardware development iterations. Correlation algorithms relate TEM cell measurements to standard open-area test site or anechoic chamber field measurements. Automated test scripts sweep input RF frequencies to locate specific emission peaks across the board circuit layout.
