Energy Fundamentals of Radio

Chapter 11Transmitter Structures

In a radio link, it is the transmitter (labeled TX in many diagrams up to this point) that dominates the power consumption. It is here that our bits of information are imposed as modulation on a sinusoidal carrier. This modulated carrier is then used to accelerate charges in the antenna, which radiates Poynting flux out into the world. Radio transmitters are rare among electronic systems in that they process both information and energy at the same time.¹

A start to understanding the energy fundamentals of radio is found in the Shannon limit, which tells us that information capacity goes up logarithmically with transmit power. Our first refinement to that rudimentary understanding comes from applying the Friis equation, which brings in the impact of the carrier frequency, antenna gain, and distance on the energy consumption (see Section 8.5.) The reader should understand this chapter as supplying a new and messier piece to the puzzle, which is the energy impact that we feel because of circuit implementation choices. This aspect of the problem is supremely uninteresting to the theorists, in love as they are with Nature’s limits. How, they ask, do we know that our implementations are the best that Nature allows? The answer is that we don’t always know. As a practical matter, though, we cannot sit around and be paralyzed by this uncertainty. When pure theory does not give us the answers, we forge ahead with what we know from experience. In this chapter, ...