Introduction

In this and the following chapter, a study of large circular dipole arrays with one or two elements driven is presented. The top view of such an array is shown in Fig. 11.1a, and a realization of a large circular array with one element driven [1] by monopoles over a ground plane is shown in Fig. 11.1b.

The main reason for initiating the study was the belief that such arrays should possess very narrow resonances if the many parameters of the problem are properly chosen. It was further believed that some particular shapes of non-circular closed-loop arrays might produce a superdirective field pattern. The large circular array of this chapter is the simplest form of the more general closed-loop array. The latter is a subject of ongoing research.

It was seen in Chapter 4 that circular arrays of a small number of elements possess noticeable resonances; previous studies also supported the idea of the existence of very narrow resonances in large circular arrays. For instance, it was known that the long Yagi array may be thought of as a surface-wave structure [2]. Such a structure does not radiate broadside, and it was observed experimentally that this property is preserved if the array is bent into a semi-circle of sufficiently large radius [3].

Essential initial considerations concerning resonances in large circular arrays came from studies in quantum mechanics.