A log-periodic antenna for pulsed electromagnetic susceptibility testing

An antenna was required for pulsed radiation, having a directive gain and a small physical aperture, to aid arraying at a later stage. The log-periodic dipole antenna (LPDA) was chosen for study as its end-fire structure minimises the physical aperture and it has a much better directivity and higher efficiency than, for example, designs based on lossy dipoles. A time-domain integral-equation program was used to investigate the behaviour under pulsed excitation. It was found that the traditional feed method for the LPDA, using a transmission line fed at the `nose', led to frequency-dependent time delays in the more distant elements, which caused dispersion of the pulse. A scheme for independent feeding of the elements was thus derived and a design with low dispersion found by iteration. An experimental realisation of the antenna showed good agreement with the predicted properties. It was also found that the antenna displayed a degree of directivity.