Antennas for satellites: Around the world with antennas made for three-axis stabilized spacecraft

Antennas for three-axis stabilized spacecraft that are in circular orbit and must communicate with one or more earth-based antennas are discussed. Antennas for many military satellites of a classified nature and for NASA´s deep space probes are excluded. The fundamental characteristics of an antenna, namely radiation pattern, directivity, gain, and polarization, are defined. These properties are discussed in relation to the dipole and the conical spiral, both low-gain antennas. A consideration of the nature of the transmission of information over long, free space paths reveals that high-gain antennas are required when the information data rate is high, as in color TV transmissions. Some typical satellite antennas are briefly described, including those of the Global Positioning System´s Navstar and the Telecommunications Data Relay satellites.