Book Review

Electrically Small, Superdirective and Superconductive Antennas
by R.C. Hansen
Publisher: Wiley Interscience, 2006

I can’t remember when was the last time, if ever, that a book on antennas was reviewed for the EMC Newsletter. In EMC, there is not much we can do about intentional radiators. We tend to leave the subject of antennas for the antenna engineers, and we always try to get away from or suppress unintentional antennas. So, who cares about studying them?
My motivation for reviewing this book was based upon the fact that it deals specifically with “small” antennas, the kind of un-intentional antennas that most often we find in EMC (small monopoles, dipoles and loops). For example, a cable radiating common mode current is a small monopole (length of cable is usually << its radiating wavelength), and the radiation from a PCB can be modeled as a small loop antenna. This book addresses only intentional radiators but most of the principals, I think, are applicable also to un-intentional radiators.
I have to confess that I had to refresh my memory over the stuff I learned twenty years ago about antennas. I took a one-year course on antennas about twenty years ago when I was a graduate student; that was basically my only background when I read this book. However, the book is written in a very readable fashion without complex derivations and to the point. If I had no problems understanding the material, you should not either. The book is short, only about 160 pages, and as I previously stated, it is very much to the point, providing the most important parameters of the basic types of small antennas (loops, dipole, monopole and their derivatives) without complex math derivations, but instead they are often intuitively explained. The most impressive aspect of the book is its large number of references quoted throughout the text; for example, chapter 1 has 198 references—all quoted in the text. These references probably cover the complete history of small antenna research since the late 1940’s to the present. Another characteristic of this book is that the author provides a “historical flow” of small antennas development throughout the years, including many examples of “small antenna blunders” that have been built, also throughout the years.
The book is only three chapters. Chapter 1 is the largest chapter in the book. It begins with the fundamental limitations of bandwidth and matching, and then provides detailed discussions on the design of loaded dipoles, ferrite loops, patches and unusual substrates and dielectric resonator antennas. An interesting section on fractal antennas is also provided. I actually thought fractal antennas had an improved performance, but it turns out the better antennas are the simplest antennas. As previous stated, the author discusses several examples of antennas that are based on good physics but are poor performers (I think fractals fall into this category) as well as design examples of antennas that are based on both poor physics and poor performance.
Chapter 2, which is the second largest chapter in the book, discusses superdirective antennas. Small dipoles and loops are superdirective; their directivity remain 1.5 as size decreases, but their efficiency also decreases. Excessive array superdirectivity (most arrays are made up of small dipoles or loops) inflict major problems in the efficiency of antennas (low radiation resistance) and narrow bandwidth. Superdirective antennas have limitations in their capabilities of bandwidth, efficiency and tolerances. The author also explores the magnification of intrinsic matching loss due to large mismatches and evaluates the recent and promising non-Foster matching circuits.
Superconducting antennas are discussed in Chapter 3. The author reviews superconductive concepts and new principles for dipole, loop and patch antennas. The author concludes with a discussion of superconductivity delay for wideband phase array steering.
If you need to get a good background in small antennas, this is a very good and useful book. If you need to research the topic further, the references in this book will keep you busy for months. EMC

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