Satellite Antenna Propagation Techniques

The troposphere extends to a height of around 10 km, and in this area, the bending of radio waves by divagation (tropospheric refraction) causes the distance of the radio horizon to exceed the optical horizon. The stratosphere extends to a distance of approximately 1060 km to a higher place the earth's surface, and the temperature in this region remains intercoursely constant. The ionosphere then extends from 60 to 1,000 km above the surface of the earth and contains several diametric layers in which ionization (the splitting of molecules into positive and negative ions) occurs. The front line of free electrons in the ionosphere has a significant effect on the propagation of radio waves. Ultraviolet rays from the sun cause this ionization.

incisive ionizing agents exist in the upper most levels of the ionosphere, but there is very little zephyr so that the ionization concentration (the number of electrons per unit volume) is low. At lower heights, atmospheric shove and ionization increase until electron density reaches its maximum level. infra this height, atmospheric pressure increases even as ionization decreases from a loss of energy (www.gordon.army.mil).

NASA's Advanced Communications Technology orbiter (ACTS) Program was developed to help the U.S. industry maintain a preeminent position in the field of beam communication theory by developing advanced technologies and proving them in actual user trials. In its first year of operation, the ACTS Program showed that it h

* Broadband video and high rate data to aircraft

Another investigation of antenna propagation and the effect of the atmosphere on the resulting signal examined the Doppler spreading on HF signals over high latitude paths. The high latitude ionosphere within the aurorean zone is known to be a highly active and disturbed medium with the potential to severely degrade the cognitive process of HF radio signals reflected from the ionosphere within this region. Aspects of the signal which may be affected include signal strength, fading rate, direction of arrival,a nd the relative relative frequency range over which the signals propagate.

Irregularities are contained within the ionosphere in the high latitude regions, and it is often seen as providing a approximate reflecting surface for obliquely propagating HF radio waves. At the same(p) time, movements in the ionosphere at reflection points create large Doppler frequency shifts and spreads onto the signal, and these effects and the associated propagation phenomena may severely limit the implementation of HF radio systems, degrading much(prenominal) things as the might of HF radio links, especially those employing modern, high speed modem engineering science (Warrington, Jones, and Dhanda, 1997, 215). Studies show that the level of Doppler spreading can be quantified and that the frequency dispersion is very sensitive to the geometry of the propagation path relative to the auroral oval. This knowledge could be incorporated into propagation models to take care in the management and planning of HF circuits to facilitate such things as appropriate choices of modulation format to maintain decorous communications with the high levels of Doppler spreading observed (Warrington, Jones, and Dhanda, 1997, 220).

A in the altogether way of using GPS signals for spaceborne attitude determination and precision hole was suggested in 1995 in an article which discussed how the Tensor program may counter at least four other methods of traditional satellite attitude and orbital determina
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