An antenna can be thought of as the control unit between a source and some medium that will propagate an electromagnetic wave. In the case of a wire antenna, it can be seen as a natural extension of the two-wire transmission line, and, in a similar way, a horn antenna can be considered a natural extension of the waveguide that feeds the horn.

The radiation properties of antennas are covered in Chap. 16.1. They include gain and directivity, beam efficiency, and radiation impedance. Depending on the antenna application, certain parameters may be more important. For example, in the case of receiving antennas that measure noise signals from an extended source, beam efficiency is an important measure of its performance.

Chapter 16.2 examines the various types of antennas, including simple wire antennas, waveguide antennas useful in aircraft and spacecraft applications, and low-profile microstrip antennas.

Finally, Chap. 16.3 treats the propagation of electromagnetic waves through or along the surface of the earth, through the atmosphere, and by reflection or scattering from the ionosphere or troposphere. More details of propagation over the earth through the nonionized atmosphere and propagation via the ionosphere are covered on the accompanying CD-ROM. D.C.

In This Section:

On the CD-ROM: