Super High Frequency - Propagation

Propagation

Radio waves in the SHF range propagate entirely by line of sight; groundwave and skywave ("skip") propagation do not occur. Although they can penetrate building walls enough for useful reception, unobstructed rights of way cleared to the first Fresnel zone are usually required. Wavelengths are small enough that they can be focused into narrow beams by parabolic and horn antennas from a half meter to five meters in diameter. Therefore they are used in point-to-point terrestrial communications links limited by the visual horizon (about 40 miles). Such high gain antennas allow frequency reuse by nearby transmitters. The size of SHF waves allow large reflections from metal objects the size of automobiles, aircraft, and ships, and other vehicles. This, the narrow beamwidths possible with high gain antennas, and the low atmospheric attenuation as compared with higher frequencies make SHF frequencies very useful in radar. Attenuation and scattering by moisture in the atmosphere is a factor at the high end of the band.