Electromagnetics Explained

11 ANTENNAS: HOW TO MAKE CIRCUITS THAT RADIATE

In Chapter 5, I discussed how and why circuits radiate, without any regard to practical implementation of antennas. This chapter covers how to make circuits that radiate efficiently. In Chapter 5, I based the results on an ideal line of current. In practice, circuits usually have a return current that flows in the opposite direction of the signal current. For example, in a two-wire transmission line, the two wires are parallel with signal current flowing in one direction and return current flowing in the opposite direction. There is a field between the wires and in the immediate vicinity of the wires, but at far distances, the fields from the two wires tend to cancel one another. The result is that ...