4.1 Introduction

This chapter describes types of lines which may perhaps be regarded as "hybrids" of those discussed in the two preceding chapters, since, of the two conductors which constitute each line, one is circular and the other rectangular in cross-section.

This, unfortunately, increases the difficulties of analysis, and this is reflected in the fact that, to the author's knowledge, no general, exact analysis has yet been given for any of the lines to be described: not even for the most symmetrical form, the square slab-line described in Section 4.2.

Nevertheless, highly accurate formulae and other data are available, and will be presented here.

From a practical constructional viewpoint, the lines treated in this chapter can in certain respects be regarded as combining the advantages of those lines treated in the previous chapters: broadly speaking (depending on tolerances and quantities required) it is easier and cheaper to produce rods of circular cross-section (by turning or grinding processes) than it is to produce rectangular strip conductors (by milling and/or cuffing processess). Similarly, it is easier, and usually cheaper, to produce outer conductors having flat, plane bounding surfaces than it is to produce those of cylindrical form, unless the required dimensions of the latter happen to be those of one of the standard production sizes of drawn tubing.

Furthermore, for those applications, such as high-power transmission, which require an appreciable centre conductor thickness (as opposed to those which can make use of printed circuit techniques), a more rugged structure is realizable by...