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Near-Earth Radio Frequency Propagation
NAVAL RESEARCH LAB WASHINGTON DC
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The Near-Earth Propagation NEP program at NRL is investigating the unique radio frequency RF phenomena that occur within one meter of the Earths surface. In the past, researchers have generally focused their propagation analysis on signals that propagate significantly above the Earths surface. However, with tomorrows distributed and integrated micro-sensors, long-range, medium-altitude communication will not necessarily be the norm. This article discusses some of the physical phenomena associated with near-Earth propagation. When radiating near the Earth, a communications link is subjected to a number of physical impairments, including Fresnel region encroachment and multipath reflections. The NEP program collected a variety of RF propagation observations in a controlled anechoic chamber at NRL, and in the open atmosphere in a variety of environmental conditions at Marine Corps Base Quantico, VA, and White Sands Missile Range, NM. The signal variation was measured in the 400 MHz, 1.78 GHz, and 2.4 GHz RF spectral regions with monopole and horn antennas at several heights above the surface and as a function of antenna-receiver separation. In this way the authors observed the influences of surface roughness, heating, and cooling on changes in the radiation pattern of the emitted RF signal.
APPROVED FOR PUBLIC RELEASE