Approaches to Determine the Transfer Function of TEM Waveguides

The standard IEC 61000-4-20 [1] describes the validation of TEM waveguides in respect to the present TEM mode and uniform area, which implies the deviation of the primary E-field component for a constant forward power. Concerning immunity tests, for which transient high-altitude electromagnetic pulses (HEMP) are supplied to TEM waveguides [2], and general measurements with the topic of intentional and unintentional electromagnetic interference (IEMI/EMI), for which arbitrary ultra wideband signals are used, the specifications according to the IEC 61000-4-20 are not sufficient. The transmission characteristic of the TEM waveguide has to be validated for any arbitrary signal, what results in a huge effort in measurement and time. The knowledge of the transfer function would reduce this effort. The advantages and disadvantages of time and frequency domain approaches for evaluating the transfer function of TEM waveguides, especially G TEM cells, are discussed in this paper.