EMP Response Prediction for Closely Spaced Monopole-Type Structures

Abstract

In considering the problem of the response of a set of whips or monopole-type structures to an. EMP event, it is not always possible to neglect the interaction of nearby elements. Situations where mutual interaction must be considered occur where a large number of antennas are installed in close proximity as on board a ship and in circular arrays. Other possibilities are the "Antenna Farm" and a parking lot where there are light poles relatively near one another. This paper develops the theory for determining the open circuit voltages and short circuit currents for such a collection of "antennas" with special attention to the Circularly Disposed Array Antenna (CDAA) or Wullenweber. In most instances, the effects of interaction of nearby objects with an antenna in the presence of an EMP event may be neglected without serious error. However, in some cases, the field itself is quite well defined, more so than is the case of the "statistical event" used in most EMP assessments, and the elements of the victim field are sufficiently close that strong interactions may be expected. It is the latter situation which has recently become of interest and to which the methods outlined in this paper are directed. The solution is given in the frequency domain, but may be readily converted to the time domain by well-known methods.