3.1 Introduction

Unlike some of the lines discussed in Chapter 2, all of those to be treated in this chapter can unquestionably be described as microwave transmission lines.

Some, of course, are more widely used than others: particular mention should be made of the widespread use of triplate (Section 3.5) striplines in the production of cheap, high-quality, miniaturized microwave systems, particularly for use in the low GHz range of frequencies. Microstrip (Section 3.6), too, has recently been under intense investigation and development as a means of producing microwave integrated circuits for use at frequencies as high, in some instances, as 70-100 GHz.

Each of the lines described below has its own set of advantages and disadvantages, which dictate its suitability for one specialized application or another the purpose here is not to discuss these, but to present the performance characteristics of each type so that the systems designer will be enabled to make his own choice.

Following the pattern already laid down, the discussion opens with a treatment of the most symmetric form, namely, the square coaxial line.

However, the analysis of this, and of some of the related types of line, involves the use of elliptic integrals, so, for future reference, the chapter begins with a brief discussion of these functions and a statement of relevant formulae, together with tabulations of useful numerical data.