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12 May 2006 Near earth propagation of distributed sensors: problems and solutions
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Both the military and consumer sectors are driving towards distributed networked sensors. A major stumbling block to deployment of these sensors is the radio frequency (RF) propagation environment within a few wavelengths of the earth. Increasing transmit power (battery consumption) is not the practical solution to the problem. This paper will discuss some aspects of the near earth propagation (NEP) problem and provide a few solutions. When radiating near the earth the communications link is subjected to a list of physical impairments. On the list are the expected Fresnel region encroachment and multipath reflections along with the intriguing radiation pattern changes and near earth boundary layer perturbations. A significant amount of data has been collected on NEP. Disturbances in the NEP atmosphere have a time varying attenuation related to the solar radiation (insolation). Solutions, or workarounds, to the near earth propagation problem hinge on dynamic adaptive RF elements. Adaptive RF elements will allow the distributed sensor to direct energy, beam form, impedance correct, increase communication efficiency, and decrease battery consumption. Small electrically controllable elements are under development to enable antenna impedance matching in a dynamic environment. Additionally, small dynamic beam forming antennas will be developed to focus RF energy in the direction of need. By creating provisions for decreasing the output RF power to the level required, battery consumption can be reduced. With the addition of adaptive RF elements, distributed autonomous networked sensors can become a reality within a few centimeters of the earth.
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R. Wert, A. Goroch, E. Worthington, K. Chan, D. Tremper, and L. Schuette "Near earth propagation of distributed sensors: problems and solutions", Proc. SPIE 6248, Wireless Sensing and Processing, 624810 (12 May 2006);

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