TABLE OF CONTENTS Antennas can be broadly classified according to function as transmitting antennas and receiving antennas. Although the requirements for each function, or mode of operation, are markedly different, a single antenna may be, and frequently is, used for transmitting and receiving signals simultaneously. Many of the properties of an antenna, such as its directional characteristics, apply equally to both modes of operation, this being a result of the reciprocity theorem described in Sec 6.2.
Certain forms of interference (see Chap. 13) can present particular problems for satellite systems which are not encountered in other radio systems, and minimizing these requires special attention to those features of the antenna design which control interference.
Another way in which antennas for use in satellite communications can be classified is into earth station antennas and satellite or spacecraft antennas. Although the general principles of antennas may apply to each type, the constraints set by the physical environment lead to quite different designs in each case.
Before looking at antennas specifically for use in satellite systems, some of the general properties and definitions for antennas will be given in this and the next few sections. As already mentioned, antennas form the link between transmitting and receiving equipment, and the space propagation path. Figure 6.1a shows the antenna as a radiator. The power amplifier in the transmitter is shown as generating P T W. A feeder connects this to the antenna, and the net power reaching the antenna will...
