Overview

The general definition of a transmission line is a device that transfers energy from one point to another. If that is the case, a clip lead used in a dc circuit would satisfy that definition. For dc and low-frequency applications (e.g., audio), this is a good definition of a transmission line. Usually it is not called a transmission line but simply a wire. Regardless of the terminology, it is a transmission line for such applications. Obviously, a clip lead would not work very well for RF and microwave applications. Chapter 1 discussed how the skin effect causes all sorts of problems with high energy traveling down a transmission line if that line is not designed exactly right. If we used a clip lead as a transmission line for a 1.9-GHz application, for example, there would be very little energy at the output of a clip lead because of a number of factors. Most of those factors are due to the skin effect in the line itself. There would be power lost in the transmission line and power lost because of radiation from the line. Thus, we have to change our definition of a transmission line. To take into account all the possible arrangements for high-frequency transmission lines, we now make the definition of a transmission line as "a device used to transfer energy from one point to another efficiently."

This definition makes much more sense for all applications, including RF and microwaves. By efficiently, we mean a device with...