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View File - University of Engineering and Technology, Taxila

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FIGURE 2.1Geometry <strong>of</strong> a satellite. (Courtesy <strong>of</strong> NASA.)highest antenna. The solar arrays provide approximately 1.4 kilowatts. Themain communication antennas are a 7.2-ft (2.19-m) receiving antenna <strong>and</strong> a10.8-ft (3.29-m) transmitting antenna. We describe more about satellitecomponents’ design later in this chapter, particularlyOverall system design procedure, availability, <strong>and</strong> reliability in Sec. 2.6Antennas in Sec. 2.7Power systems in Sec. 2.8Onboard processing <strong>and</strong> switching systems in Sec. 2.9Antennas control <strong>and</strong> tracking in Chap. 3, Sec. 3.4.2Other characteristics <strong>of</strong> satellites are discussed in the next five sections.As stated in Chap. 1, a satellite comprises several individual chains <strong>of</strong>equipment called a transponder: a term derived from transmitter <strong>and</strong> responder.The block diagram shown in Fig. 2.2 may represent a transponder unit. Asseen in the figure, a transponder may be described as a system composedbasically <strong>of</strong> a b<strong>and</strong>pass filter required to select the particular channel’s b<strong>and</strong>frequencies, a frequency translator that changes frequencies from one level toanother, <strong>and</strong> an output amplifier. Once amplified, the channels are recombinedin an output multiplexer for the return transmission. All these devices must beCopyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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