Chapter Overview

Transmission lines in communication carry telephone signals, computer data in LANs, TV signals in cable TV systems, and signals from a transmitter to an antenna or from an antenna to a receiver. Transmission lines are critical links in any communication system. They are more than pieces of wire or cable. Their electrical characteristics are critical and must be matched to the equipment for successful communication to take place. Transmission lines are also circuits. At very high frequencies where wavelengths are short, transmission lines act as resonant circuits and even reactive components. At VHF, UHF, and microwave frequencies, most tuned circuits and filters are implemented with transmission lines. This chapter covers basic transmission line principles—theory, behavior, and applications.

Chapter Outline

13-1 Transmission Line Basics
13-2 Standing Waves
13-3 Transmission Lines as Circuit Elements
13-4 The Smith Chart

Chapter Objectives

• Name the different types of transmission lines and list some specific applications of each.
• Explain the circumstances under which transmission lines can be used as tuned circuits and reactive components.
• Define characteristic impedance and calculate the characteristic impedance of a transmission line by using several different methods.
• Compute the length of a transmission line in wavelengths.
• Define standing wave ratio (SWR), explain its significance for transmission line design, and calculate SWR by using impedance values or the reflection coefficient.
• State the criterion for a perfectly matched line and describe conditions that produce an improperly matched line.
• Use the Smith chart to make transmission line calculations.
• Define stripline and microstrip and state where and how they are used.