The performance properties of several electrically small, self-resonant wire antennas are compared as a function of their total wire length, geometry, and effective volume. The radiation properties considered include resonant frequency, radiation resistance, and quality factor (Q). It is shown that the resonant properties of these antennas are directly a function of the antenna's effective height and effective volume, which are established by both total wire length and geometry. When the total wire length and geometry of these antennas are configured such that the antennas exhibit the same effective height and volume, their resonant properties are essentially identical, independent of any differences in their total wire length and geometry. Both computed and measured data are presented to support the comparison of the antennas' resonant properties.

A discussion on the properties of electrically small self-resonant wire antennas

In this paper, the performance properties of several fundamental small-antenna designs are compared as a function of overall length and size (ka), where the antennas operate at or very near the same frequency. The objective of this work is to determine which basic design approach or configuration, if any, offers the best performance in terms of: achieving an impedance match; the radiation-pattern shape; the radiation efficiency; the half-power bandwidth; and the 2:1 VSWR bandwidth. The fundamental antenna designs studied here include the spherical folded helix, the cylindrical folded helix, the matched disk-loaded dipole, the matched spherical-cap dipole, and the multi-arm spherical resonator. In addition to discussing the different antenna designs, the fundamental approaches used in impedance matching and optimizing the bandwidth of these small antennas are described. Both numerical simulations and measured results are presented.

A Performance Comparison of Fundamental Small-Antenna Designs

About sixty years ago, Harold A Wheeler published a paper entitled, "Fundamental Limitations of Small Antennas." Wheeler presented formulas that related the antenna radiation Q to the physical volume of the antenna. This paper (1) briefly reviews the history of the fundamental limitations of small antennas, (2) presents Wheeler's formulas in a revised form, and (3) uses the WIPL-D computer code to validate the Wheeler formulas. The goal is to demonstrate that the Wheeler paper did, indeed, address the fundamental limitations of electrically small antennas, and that it is very useful in the understanding and quantification of these limitations

Fundamental hmrations of small antennas: validation of wheeler's formulas

The method of moments (MoM) is used to analyze the disk loaded monopole (DLM) antenna. Results were validated by comparison with mode-matching and wire-model methods as well as with measurements covering a wide range of electrical sizes. A quasistatic treatment is shown to be both rapid and accurate for the electrically small case. Equivalent circuits are obtained for predicting communication system performance. Parameters defining the fundamental limitations of electrically small antennas are extracted and shown to be accurate for system analysis and useful as design tools.

The disk loaded monopole antenna

This letter presents the design, fabrication, and experimental characterization of small spherical antennas fabricated using arrays of non-interconnected planar conductor elements. The antennas are based upon spherical resonator structures with radiation Q-factors approaching $1.5\times$ the fundamental lower limit. The antennas are formed by coupling these resonators to an impedance-matched coplanar strip transmission line. Direct electrical connection between the feed and the antenna are made only to conductor elements coplanar with the transmission line, simplifying the fabrication process. The incident energy excites a collective resonant mode of the entire sphere (an electric dipole resonance), thereby inducing currents in each of the rings of the structure. The presence of the conductor elements outside of the feed plane is critical towards achieving the excellent bandwidth behavior observed here. The fabricated antennas have a normalized size $ka=0.54$ (where $k$ is the wavenumber and $a$ is the radius of the sphere) and exhibit high radiative efficiencies ($>$ 90%) and bandwidth performance near the fundamental limit for their size.

Small Spherical Antennas Using Arrays of Electromagnetically Coupled Planar Elements

A brief account of some concepts and developments in my experience with antennas is presented under three headings: A-wide-band matching to a long line; B-small antennas; C-planar arrays. They cover the half-century from 1935 to date.

H. Wheeler

Papers

Antenna topics in my experience