Three-dimensional time-domain calculations for EMP simulators

Summary form only given, as follows. Certain electromagnetic pulse (EMP) simulators involve the discharge of a capacitor bank into a wideband antenna. This produces a burst of broad-band electromagnetic radiation, which can be used for testing equipment exposed to EMP. We have used a three-dimensional finite-difference time-domain (FDTD) code for modeling the coupling of a pulse-power generator to a TEM horn antenna. This system involves the coupling of a Marx bank to the antenna through two stages of pulse compression, viz., the ´transfer´ and ´peaking´ sections. The parameters of the pulser and antenna are broadly the same as those described previously, but with some differences. The antenna has a characteristic impedance of 90 ohms and a matching resistive termination. Simulations include only the peaking capacitor and antenna, and start at the point where the 82 pF peaking capacitor is charged to 1 MV. The simulations yield the temporal behaviour of the input current to the antenna, and the 3-D electromagnetic field structure in the near- and far-fields. As expected, this shows the effects of standing wave structures within the horn. We have also studied the effect of different kinds of termination on reflection from the aperture. Such studies could be generalized to optimize coupling to other kinds of pulsers. As a first step in this direction, we have calculated the input impedance of the antenna over its ´useful´ range of frequencies. This is useful in examining the sensitivity of the radiated EMP waveform to changes in pulser configuration, e.g., the use of different kinds of switches, or re-configuration of the Marx/peaking sections.