Publisher Summary This chapter discusses the satellite antennas. The last exit point of a satellite transmission system and the first receiving point of a satellite receiver system is the antenna. This chapter addresses some fundamentals of antenna theory and covers some issues concerning noise and cross-coupling phenomena among receiver and transmitting antennas. An isotropic antenna is defined as a hypothetical antenna having the same radiation in all directions. It is assumed that the power gain of an isotropic antenna is 1.0. A directional antenna is one that radiates or receives electromagnetic waves in some directions better than others. An omnidirectional antenna is defined as one having an essential nondirectional pattern in azimuth and a directional pattern in elevation. The radiation pattern of antennas is described in terms of lobes.