The BBHA 9120 J is a linear polarized high-gain horn antenna for the frequency range 0.8-6.2 GHz. The radiation pattern is strongly focused in the forward direction and depends on the frequency. Therefore, when used for immunity testing of an Equipment-under-Test (EuT) (in the following we will assume that the EuT has a cubical shape), a minimum distance between the front plane of the horn antenna and the EuT has to be kept in order to irradiate uniformly the whole EuT.