A Theory of Antenna Electromagnetic Near Field—Part II

Abstract

We continue in this paper a comprehensive theory of antenna near fields inaugurated in Part I. The concept of near-field streamlines is introduced using the Weyl expansion in which the total field is decomposed into propagating and nonpropagating parts. This process involves a breaking of the rotational symmetry of the scalar Greens function that originally facilitated the derivation of the Weyl expansion. Such symmetry breaking is taken here to represent a key to understanding the structure of the near fields and how antennas work in general. A suitable mathematical machinery for dealing with the symmetry breaking procedure from the source point of view is developed in detail, and the final results are expressed in clear and compact form susceptible to direct interpretation. We then investigate the concept of energy in the near field where the localized energy (especially the radial localized energy) and the stored energy are singled out as the most important types of energy processes in the near-field zone of general antenna systems. A new devolvement is subsequently undertaken by generalizing the Weyl expansion in order to analyze the structure of the near field, but this time from the far-field point of view. A hybrid series combining the Weyl and Wilcox expansions is derived, after which only the radial streamline picture turns out to be compatible with the far-field description via Wilcox series. We end up with an explication of the general mechanism of far-field formation from the source point of view. It is found that the main formative processes in the antenna near-field zone are reducible to simple geometrical and filtering operations.