JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year SATELLITE COMMUNICATIONS Previous Question Paper (June - 2024 - R18)

In the context of an elliptical orbit, the points of extreme distance between the satellite and the center of the primary body (Earth) are defined as follows:

• Perigee: This is the point in the satellite's orbit that is closest to the center of the Earth. At this position, the satellite possesses its maximum orbital velocity according to Kepler's second law.
• Apogee: This is the point in the satellite's orbit that is farthest from the center of the Earth. At this position, the satellite moves at its minimum orbital velocity.

These two points define the major axis of the elliptical orbit, and the distance between them is equal to twice the semi-major axis (2a).

The elevation angle is defined as the vertical angle between the local horizontal plane of an Earth station and the line-of-sight path to the satellite. It is a critical parameter in satellite communications as it determines the length of the signal path through the Earth's atmosphere and the amount of interference or blockage caused by local terrain or buildings.

A higher elevation angle results in a shorter path through the atmosphere, which reduces atmospheric attenuation, scintillation, and gaseous absorption. Conversely, very low elevation angles increase the slant range and the thickness of the troposphere the signal must traverse, leading to increased signal degradation.

• The Earth station is located at point O.
• The horizontal plane is the tangent to the Earth's surface at point O.
• The elevation angle (EL) is the angle measured upward from this horizontal plane toward the satellite.
• The zenith angle is the complement of the elevation angle, measured from the local vertical (zenith) down to the satellite.