1.1 Introduction

The aim of this chapter is to revise the basic principles of transmission lines in preparation for many of the chapters that follow in this book. Obviously one chapter cannot cover such a wide topic in any depth so at the end some textbooks are listed that may prove useful for those wishing to go further into the subject.

Microwave measurements involve transmission lines because many of the circuits used are larger than the wavelength of the signals being measured. In such circuits, the propagation time for the signals is not negligible as it is at lower frequencies. Therefore, some knowledge of transmission lines is essential before sensible measurements can be made at microwave frequencies.

For many of the transmission lines, such as coaxial cable and twisted pair lines, there are two separate conductors separated by an insulating dielectric. These lines can be described by using voltages and currents in an equivalent circuit. However, another group of transmission lines, often called waveguides, such as metallic waveguide and optical fibre have no equivalent circuit and these are described in terms of their electric and magnetic fields. This chapter will describe the two-conductor transmission lines first, followed by a description of waveguides and will end with some general comments about attenuation, dispersion and power. A subsequent chapter will describe the properties of some transmission lines that are in common use today.

1.2 Lossless Two-Conductor Transmission Lines - Equivalent Circuit and Velocity of Propagation

All two-conductor transmission lines...