Field uniformity in standard TEM cells

The longitudinal and transverse field characteristics of a standard TEN cell rated to 200 MHz are described. Data was collected using a 3 axis electric field probe optically coupled to control instrumentation. Several instances were investigated. First, power requirements to establish a theoretical 70 Volt/meter field in the cell were determined. Using these settings, the field was then measured in a volume consisting of 40 individual points. In a second series of measurements, the field was measured in the volume surrounding a metallic DUT. Thirdly, the TEM cell structure was studied analytically to determine the current density distribution in the septum and top and bottom walls. The data reveals field gradients in the central volume of the cell and a resonance at 161 MHz that is positionally dependent. In addition, field uniformity is shown to be quite good until 161 MHz. Beyond 161 MHz, the field gradients increase.