Application of reflection and diffraction techniques to the analysis of an EMP simulator

The response of a parallel-plate transmission-line electromagnetic pulse (EMP) simulator to continuous wave excitation in the very high frequency (VHF) region is analyzed. A reasonably accurate prediction of response irregularities measured in an operational EMP test facility is obtained using a combination of geometrical optics and geometrical diffraction theory. The analysis predicts that multiple internal reflections were primarily responsible for observed irregularities at the measurement positions. While an analysis based upon optical techniques involves different approximations and assumptions than alternative methods, such as the method of moments, the optical approach was found to be more practical in the VHF regime and, perhaps more importantly, allowed identification of the dominant physical mechanisms which cause deviations from the ideal field quality desired of the facility in the VHF region. Based upon these calculations, the simulator was modified to reduce internal reflections, and subsequent measurements have confirmed the usefulness of the theoretical predictions.