Enhanced estimates of field distribution's uncertainty contribution for TEM waveguides

The expanded measurement uncertainty of both the measurement of radiated emission and the measurement of electromagnetic field immunity depends mostly on the field distribution within the testing volume. In general, that uncertainty contribution has to be estimated from sampled measurement data. In most cases this results in an overestimation. The estimate can be reduced by exact knowledge of the field distribution and extensive measurements. In this paper a method is described, that calculates enhanced estimates from the calibration data of the test method. This calibration data has to be measured for the validation of the test volume and thus there is no need to perform another extensive measurement to calculate the uncertainty contribution. The enhanced estimate is obtained from the combination of analytical knowledge of the theoretical field distribution, measurement data and stochastical methods. The theory explained in this paper is applied to the calibration data of a GTEM 1250. It is shown, that the estimates are in good agreement with uncertainty contributions obtained from more extensive measurements.