Broadening of antenna patterns during transhorizon tropospheric propagation and the problem of electromagnetic compatibility

In EMC analysis, the noise signal is usually determined with allowance for the antenna radiation patterns, under the assumption of free-space operation. Since the free-space condition does not occur in practice, considerable broadening of the antenna pattern may occur in the case of transhorizon tropospheric propagation. With reference to antenna pattern broadening in the EMC problem, experimental data obtained for many paths of various lengths and different frequencies are examined. It is shown that a narrow-beam antenna pattern at the 3 dB level is at least 1.7 deg in the vertical plane and 1 deg in the horizontal plane, regardless of the pattern width in free space.