View File - University of Engineering and Technology, Taxila

We can conclude that the antenna must be pointed toward a compass headingof 164:7 and be adjusted to an elevation of 48:68 to transmit or receivesignals from the satellite in the geostationary orbit.2.5 SWATH WIDTH, COMMUNICATION TIME,AND SATELLITE VISIBILITY2.5.1 Visibility of Satellites from the EarthOne of the most important pieces of information about a communicationsatellite is whether it can be seen from a particular location on the earth. Theuse of (2.21) and (2.22b) enables us to interpret the bearings relative to thelocal meridian. As an illustration, suppose L ET ¼ 40 and D ¼ 50 . Consequently,a z ¼ 62 and the elevation of the satellite y ¼ 21 . Now, on the onehand, suppose the satellite is east of the earth station and the station is south ofthe equator; the azimuth of the satellite from the station will equal a z , that is,62 E of N. On the other hand, if the station is north of the equator, then theazimuth of the satellite is ð180 a z Þ¼118 E of N. Similarly, if the satellite iswest of the station, then the azimuth of the satellite is ð180 þ a z Þ¼242 EofN for the station north of the equator, and finally ð360 a z Þ¼298 E of N fora station south of the equator.2.5.2 Communication TimeThe amount of time t p an earth station is required to communicate with anorbiting satellite as it passes overhead is given bywheret p ¼g180 t s1 ðt s =t e Þt s ¼ orbit period.t e ¼ rotation period of the earth ¼ 1 sidereal day.ð2:24ÞNote that the sign depends on whether the satellite is in a retrograde(opposite-direction) orbit or a prograde (same-direction) orbit. For instance, ifa satellite is in a prograde orbit, t e ¼ t s , and as such t p ¼1. The expression(2.24) is valid for a satellite orbiting at altitude h 0 and passing over any pointon earth with an elevation angle exceeding y.Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.