Limitations on vertically polarized ground-based antennas as gain standards

Ground-based monopoles are not suitable standard-gain antennas because their power gain, at low elevation angles especially, is much less than that for the same monopole fed against infinite perfectly conducting ground, and the power gain achieved may vary as much as 3 dB or more as the moisture content of the ground changes. Low-angle approximations are given to show the effect of reflection coefficient on power gain for a quarter-wave monopole fed against a ground plane on imperfect ground and a horizontal half-wave dipole above imperfect ground. Low-angle dipole power gain variations are several tenths of a dB; monopole variations are several dB for ground constants varying from
\epsilon_{r} = 4, \sigma =0.02
mho/m to
\epsilon_{r} = 10, \sigma = 0.06
mho/m. Monopole power gain data are grouped according to test range moisture conditions at the time of measurement, and a statistical analysis of the resulting data is briefly discussed.