Practical Antenna Handbook 5/e, 5th Edition

CHAPTER 3Antenna Basics

An antenna is an example of a transducer—a device that converts one form of energy to another. Other examples include audio loudspeakers (electronic signals → sound waves), thermocouples (temperature changes → electrical signals), and woodstoves (stored chemical energy → heat).

An antenna converts time-varying electrical currents that are confined and guided within a circuit or transmission line to a radiated electromagnetic wave varying at the same rate and propagating outward through space—completely independent of the circuit that produced it. It is not unreasonable to visualize this process as “freeing” the electromagnetic waves created by the time-varying currents and “launching” them into space—much like a slingshot ...