Look Angles

To ensure that an Earth station antenna has the center of its main lobe (the antenna boresight) pointed accurately toward a satellite, it is necessary to know the angles of elevation and azimuth (the look angles) of the satellite relative to the Earth station. Elevation is the angle between the line of sight from an Earth station to a satellite and the local horizontal plane (horizon) at the Earth station. Azimuth is the horizontal angle, measured in the local tangent plane at the Earth station, between a reference direction (usually true north) and the projection of the satellite line of sight onto that plane. For geostationary satellites, look angles are fixed for a given Earth station location, whereas for non-geostationary systems they vary continuously with time.

The look angles, particularly elevation, strongly influence propagation losses and minimum look-angle constraints, particularly at higher frequencies. To calculate the path loss, we also need to know the slant range from the Earth station to the satellite.