TABLE OF CONTENTS The energy in electro-magnetic phenomena is mechanical energy. The only question is, Where does it reside? On the old theories it resides in electrified bodies, conducting circuits, and magnets, in the form of an unknown quantity called potential energy, or the power of producing certain effects at a distance. On our theory it resides in the electro-magnetic field, in the space surrounding the electrified and magnetic bodies, as well as in those bodies themselves....
James Clerk Maxwell, 1865
This chapter treats antennas as converters of electromagnetic energy. From this perspective, an antenna is a device that converts guided, bound, or reactive electromagnetic energy into unbound, or radiation, electromagnetic energy. Electromagnetic energy analysis is not commonly applied in antenna theory. Thus, this chapter begins by motivating the subject, discussing the value of examining fundamental antenna physics. Then, this chapter considers localization of electromagnetic energy and develops an understanding of how bound electromagnetic energy uncouples and radiates away. Unlike the more traditional analytic techniques presented in the last chapter, analysis of electromagnetic energy flow leads to novel antenna designs that conform to these flows. Finally this chapter uses energy-flow techniques to derive fundamental limits to antenna size and performance.
Traditional thinking about antennas treats them as radiators and receivers of electromagnetic fields as described by Maxwell's equations. This approach does a remarkable job of analyzing real-world antenna problems and providing correct answers. Why then should one study a seemingly esoteric subject like electromagnetic energy flow?
This question may be answered...
