Expanding the Bandwidth of TEM Cells for EMC Measurements

This paper discusses the development of a modified (absorber-loaded) transverse electromagnetic TEM cell with expanded bandwidth for use in accurately characterizing electromagnetic interference (EMI) fields within a shielded environment. The cell is analyzed experimentally, both before and after the modification, to determine its radio-frequency (RF) characteristics, both as an RF transmission line and as an electromagnetic (EM) field simulator or detector. Comparative measurements are given to show the performance of the modified versus the unmodified cell in parameters such as voltage standing-wave ratio (VSWR), insertion loss, test-field uniformity, and reverse-coupling characteristics. The results of these measurements indicate an approximate two-fold increase in the upper useful frequency of the modified cell. An example of using the cell to evaluate the radiated emissions from a common electronic module (microprocessor timing circuit) is given. Finally, the technique of absorber loading is extended to larger cells, specifically a 3- × 3- × 6-m cell.