Chapter 3
Antenna Theory and Design

It’s an amazing kind of sorcery that you can point a piece of metal at the sky, attach it to some various electronic bits and pieces, and suddenly listen to a radio broadcast from the other side of the planet.

That piece of metal pointed at the sky is the antenna. As you may have guessed, when it comes to receiving radio signals from space (or from anywhere else, for that matter) the kind of antenna—the shape and size, and the direction in which you point the antenna—is very important. Before we get into the various types of antennas that work best for SDR, I’d like to briefly discuss how antennas work.

We could talk about the physics of antennas for an entire book, and there are entire textbooks and courses of study about the subject. But that would be way outside the scope of this book, and unnecessary. This chapter is just meant to give you an introduction to how antennas operate for both sending and receiving. We’ll briefly discuss how antennas transmit a signal, why you need different kinds of antennas to receive those signals, and what kinds might work best for the particular projects in this book.