The tricky coupling of the EMP with a UHF antenna on a mast

Coupling of the electromagnetic pulse (EMP) to UHF antennas on masts can be misleading, because the resonant frequency of the induced current (and often that of the voltage of the termination) is determined by the structure dimensions (antenna-plus mast) and not by the antenna characteristics. In most cases this frequency is out-band with respect to the UHF-band of the antenna. Measurements were performed to study these coupling effects. The induced voltage waveform on the 50 Omega termination was directly related to the waveform of the current on the outer shield of the cable. Because of the rather small dimensions of the antenna/cable combination, the induced signals were not dependent on the length of the simulated pulse, but only on the rise-time and peak value.<>