Satellite antenna propagation
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Satellite antenna propagation involves a number of techniques and different ranges for sending and receiving signals. New measurement techniques for testing antennas ar also being developed and implemented to analyze the propagation field and to understand what happens to the signal under different conditions. The ACTS system is one important technological system being used by more and more companies and the U.S. government to place satellites in orbit, to identify and secure those orbits, and to communicate on various levels. The transmission of electromagnetic waves through space has become common over the past century. The antenna is the critical interface between the hardware and space, and antenna testing is a major field to assure that the antenna performs the desired task and does so at the proper levels, in the correct range, and so on: "Antenna design and propagation predictions are the key to successful HF communication" (www.gordon.army.mil). An examination of the issues raised with reference to antenna propagation and the measurement of performance shows the nature of the field today and some of the directions in which it is moving.HF transmissions (sky waves) are affected to a great degree by the earth's atmosphere. HF communications would be easy if the atmosphere were static, but in fact the atmosphere varies with altitude, location, time of day, season, and year. The layers of the earth's atmosphere and their properties also affect radio wave propaga
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originally used acquired ranging signals from a GPS constellation of only five or six functioning satellites. Today, onboard GPS receivers gather signals from an essentially complete 24 satellite GPS constellation. Early spaceborne receivers weighed approximately 28 kilograms, while modem units are often under three kilograms. Antennas set to receive GPS signals have been placed as the satellite orbited a circular, sun synchronous pattern of 380 nautical miles. The Landsat antennas used to pick up the GPS signals were mast mounted to connect the high gain antenna to the main body of the satellite. However, engineers at Magnavox estimated that, with a 16 to 19 GPS operational satellite constellation, the spaceborne receiver would yield orbital positioning errors of less than 10 meters. Logic upsets caused by various highly energetic charged particles careening though outer space also affected the antenna array. Changes in equipment have provided the means to obtain a more accurate and well behaved series of position and velocity solutions. Today, signals from Navstar GPS provide excellent positioning accuracies when used to navigate properly equipped space vehicles at orbital altitudes lower than the GPS satellites, and
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, Gedney Gargione, Ikeda Yamauchi, Rogers Jones, Simunic Koren, Navstar GPS, ACTS Program, Jones Dhanda, Polytechnic Institute, Definition Television, antenna propagation, hf radio, propagation vol 144, proceedings microwave antenna, vol 144, iee proceedings, microwave antenna, proceedings microwave, antenna propagation vol, electric field, iee proceedings microwave, propagation vol, microwave antenna propagation, satellite communications, radio waves,
Approximate Word count = 2561
Approximate Pages = 10 (250 words per page)
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