October 1969 | NTIA Technical Memo ERL TM ITS 206
Laurance G. Hause; F. George Kimmett
Abstract: Ground-to-ground path loss measurements are tabulated and discussed for paths terminated in surface and buried antennas, with and without security fences. Both horizontally and vertically polarized antennas at 415.9 MHz were used. Path lengths varied from 15 m to 17 km, and depths ranged from 0 to -2.25 m. Conical pits 3 m deep were dug into the earth and filled with fuel oil, which served as a homogeneous dielectric surrounding the antennas and formed a smooth, level boundary layer at the surface. For low antennas, off-path terrain reflections can be the dominant mechanism in rough terrain. The probability of this increases as antenna height above ground decreases. Only antennas having mainly upward-directed patterns should be used in the buried antenna configuration in the 230-400 MHz band. Annular slot antennas 1 m below the surface have transmission loss about 20 dB greater than monopoles 0.75 m above ground. Transmission loss between annular slot antennas increases by 6 dB for each meter increase in depth.
Keywords: buried antennas; path loss measurements; boundary layer; security fences
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