TABLE OF CONTENTS This chapter provides a basic engineering overview of satellite antennas. The performance of a satellite link depends in large measure on the antenna system.
The antenna is an electrical conductor (or conductors) that radiates electromagnetic energy into space (transmission) and/or collects it from space (reception). Antennas are transducers that transfer electromagnetic energy between a transmission line and free space. A transmitting antenna behaves like an equivalent impedance that dissipates the power transmitted; the transmitter is equivalent to a generator. A receiving antenna behaves like a generator with an internal impedance corresponding to the antenna-equivalent impedance. The receiver represents the load impedance that dissipates the time averaged power generated by the receiving antenna [AMA200101]. See Figure 3.1.
Antennas are reciprocal devices. It means that they can be used both as transmitting and receiving elements; in two-way communication, the same antenna can be used for both transmission and reception (receiver protection may be used in some cases). For example, this is how the antennas on cellular phones operate. The reciprocity principle affirms that the transmitting and receiving patterns of an antenna are identical at a specified wavelength; there is no functional difference between receive and transmit modes of an antenna except that the power flow is directed inwards to the receive antenna and outwards from the transmit antenna. An antenna has the same efficiency, directivity, and polarization characteristics in receive and transmit modes. This property is called reciprocity, and it occurs due to the...
