Abstract
Transverse electromagnetic (TEM) waveguides are predominantly used for emission and immunity tests. General requirements for TEM waveguides are given by the IEC 61000-4-20. Annex C of the IEC 61000-4-20 specifies immunity tests based on high-altitude electromagnetic pulses with a double exponential waveform. This waveform's shape is sufficiently defined by the rise time and the pulsewidth. The quality of its transmission within a waveguide can, thus, be expressed by the allowed variation of these parameters. However, other arbitrary signals cannot be reduced to just these characteristic parameters. In this paper, a method is described that offers the possibility to characterize the transmission quality of a TEM cell for arbitrary transient waveforms. It is based on the Pearson correlation coefficient of a so-called reference signal and the signals being measured within the test volume of a TEM cell. Both signals are measured simultaneously with identical field probes in order to be independent from the reproducibility of the signal generator. The signals are windowed and limited to include only the defining reflections and distortions. By means of this signal-dedicated validation procedure, the transmission quality of a TEM waveguide can be validated for an arbitrary transient waveform
Highlights
W ITH their high degree of interconnectivity, modern electronic systems are prone to intentional or unintentional electromagnetic interference (IEMI)
The performance of two identical field probes in both measurement positions is suggested to reduce the mathematical effort of correcting the measured field signals. They have to be small in comparison to the cross section of the waveguide in order to avoid field distortions, and their bandwidth shall cover that of the arbitrary transient waveform. Both field probes are mounted on a positioning system, whose shaft dimensions are equal to the probes head [see Fig. 11(b)], what reduces the measurement uncertainty caused by the field probe position
transverse electromagnetic (TEM) waveguides and their validation procedures are described by the IEC 61000-4-20
Summary
W ITH their high degree of interconnectivity, modern electronic systems are prone to intentional or unintentional electromagnetic interference (IEMI). 1) Method 1: The TEM mode—expressed by the ratio of the so-called secondary and primary field components—and the field uniformity—expressed by the standard deviation of the primary field component—are to be evaluated in a defined test section The evaluation of these two figures is mandatory for all TEM waveguide measurements and is carried out in the frequency domain (FD). 2) Method 2: For the HEMP tests, the time-domain (TD) characteristics of the waveguide are expressed by means of the rise time (trise) and the pulsewidth (tfwhm ) definitions for the electric field strength when a double exponential pulse with a defined waveform is applied to the port of the waveguide. Whereas the common procedure, performed in the FD in order to verify the basic transmission quality, is mandatory for all interference and susceptibility tests carried out with the waveguide, the HEMP validation is carried out in the TD exclusively for HEMP measurements
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