4.8 LOOKING AHEAD
This chapter examined how electromagnetic waves propagate after leaving an antenna. The next step is to examine the antenna itself—the interface between guided electromagnetic energy in conductors or waveguides and radiated energy in space.
An antenna performs the transformation between guided electromagnetic energy—confined within conductors or waveguides—and radiated energy that propagates freely through space. It determines:
- How efficiently power is transferred from transmitter to free space,
- How incoming waves are captured and delivered to the receiver,
- The direction in which energy is concentrated,
- The polarization and spatial distribution of the radiated field.
- How the reactive near field, radiating near field, and far field are distributed around the installation.
Without antennas, there is no practical means of launching or receiving propagating electromagnetic waves.
Chapter 5 therefore examines antennas as electromagnetic radiators and collectors. We will explore radiation mechanisms, current distributions, polarization, radiation patterns, directivity, gain, impedance, and bandwidth. Of particular importance to RF radiation safety are the reactive near field, radiating near field (Fresnel region), far field, beam shape, sidelobes, and the effect of installation geometry on accessible field levels.
If this chapter explained how waves travel once in space, Chapter 5 explains how they get there—and how they are captured at the far end.