An Earth station antenna typically requires a rigid steel backup structure combined with an accurate dish surface. They are fitted with necessary bearings, gears, and drives to enable pointing accuracy within a few tenths of a degree. The structure must also be able to withstand extreme weather conditions, from excessive heat to cold, and hurricanes. Three common antenna mount types are X- Y mount, AZ/EL mount, and polar mount.
The experimental results show that the A-E-axis yoke has better performance, versatility, light weight and lower cost than the X-Y axis frame in the satellite communication earth station antenna mount.
This mount is used for medium-sized antennas (10-13 meters). Figure 1. shows an X-Y mount. In this mount, the lower axis (X) is parallel to the ground. Rotation about this axis moves the antenna in elevation. The upper axis (Y) lies in a vertical plane, and is perpendicular to the X-axis. The position of the Y-axis in the vertical plane depends on the rotation of the X-axis, and can range from vertical to horizontal.
This is the simplest type of mount, but is a limited coverage mount. It provides coverage up to 90 degrees in the X-axis but, in some cases, only ± 5 degrees in the Y-axis.
The location of a point on Earth can be described by using the azimuth-over-elevation coordinate system. Azimuth is defined as an angle produced by rotation about an axis, which is perpendicular to the local horizontal plane. The elevation axis rotates in the local horizontal plane as the azimuth angle rotates. A change in the elevation angle will cause a rotation of the antenna in the vertical plane. Installation of an AZ/EL mount is relatively easy. The azimuth axis should be very nearly vertical to the local ground plane to minimize the change in elevation angle when azimuth is swept. Figure 2. shows a simplest form of AZ/EL mount. This type of mount has full elevation coverage and ± 180 degrees in azimuth.
A polar mount has two axes of rotation as shown in Figure 3. The first one is the hour angle axis, which is parallel to the Earth’s axis. It is inclined in the north-south direction from the local horizontal through an angle equal to the latitude of the site. Therefore, the hour angle axis is parallel to the ground at the equator and perpendicular to the ground at either the North or the South Pole. The second angle is the declination. Satellite longitude, Earth station longitude, and latitude determine the amount of declination required.