Experimental Validation of Performance Limits and Design Guidelines for Small Antennas

TLDR

The theoretical limits for small‑antenna performance derived by Wheeler and Chu dictate tradeoffs among size, bandwidth, and efficiency, and additional guidelines address permittivity, aspect ratio, and internal structure. The study extracts and analyzes experimental data from a large set of published designs to confirm that the Wheeler–Chu performance limits for size, bandwidth, and efficiency hold experimentally. The experiments show that these limits also apply to antennas that are not electrically small, that design factors such as permittivity, aspect ratio, and internal structure predict performance, and that antennas with low permittivity, near‑unity aspect ratio, and uniformly filling the enclosing sphere achieve the highest performance, thereby validating the theoretical guidelines.

Abstract

The theoretical limit for small antenna performance that was derived decades ago by Wheeler and Chu governs design tradeoffs for size, bandwidth, and efficiency. Theoretical guidelines have also been derived for other details of small antenna design such as permittivity, aspect ratio, and even the nature of the internal structure of the antenna. In this paper, we extract and analyze experimental performance data from a large body of published designs to establish several facts that have not previously been demonstrated: (1) The theoretical performance limit for size, bandwidth, and efficiency are validated by all available experimental evidence. (2) Although derived for electrically small antennas, the same theoretical limit is also generally a good design rule for antennas that are not electrically small. (3) The theoretical predictions for the performance due to design factors such as permittivity, aspect ratio, and the internal structure of the antenna are also supported by the experimental evidence. The designs that have the highest performance are those that involve the lowest permittivity, have an aspect ratio close to unity, and for which the fields fill the minimum size enclosing sphere with the greatest uniformity. This work thus validates the established theoretical design guidelines.