Small Antenna Design
by Douglas B Miron, Published by Newnes-Elsevier
ISBN 0-7506-7861-5, paperback, 283 pp +CD-ROM, $69.95
EN-Genius Reviewer: Dennis L. Feucht

Engineers familiar with time-domain analog circuits who are wondering what has been going on in the limelight of communications for the last 15 years will be given a jump-start by this book, at least as it applies to that quintessential element of wireless: the antenna. Miron's book is quite readable, though you can expect what is essentially applied electromagnetic fields theory throughout it. He has a few appendices for refreshing those who have forgotten how to integrate surface area in spherical coordinates. The book has plenty of those kinds of complicated formulae, with integral signs stacked at the left end, but the author does a good job of managing the interpretation of the math in practical terms. I would have preferred that he fill in a few extra steps in the math, but there are no gaping holes. The illustrations are useful and have that CAD look, as is typical of the style nowadays. This is apropos here, for Miron emphasizes the numerical calculation of antenna parameters, letting the computer do the hard math numerically. Programs are included on an accompanying CD and source-code fragments are given in the book, written in C.

A small antenna is one much less than a wavelength (<0.1 ), for which the current in the antenna can be assumed to be equal everywhere along its length. Antennae can be modeled as having two series resistances, the radiation resistance and resistive losses. Power dissipated in the first resistance, in the model, is actually the radiated power. Losses are due to wire resistance and lead to a discussion of antenna efficiency, impedance matching, directivity, gain, bandwidth, Q, and other parameters. The early emphasis in illustrating antenna principles is on dipole and loop antennas. Impedance-matching is illustrated with L sections. This is lumped-parameter circuitry but, even here, has so many reactances that it is quickly amenable to computer solution.

Ground effects and image theory for antennas using ground-planes leads into the Numerical Electromagnetic Code (NEC), a freely-released public-domain copy of which is on the CD. The program grew out of an early Antenna Modeling Program in the military, at Lawrence Livermore National Labs, and the more advanced version of NEC requires a LLNL license. The author outlines antenna design strategy in a computer age as consisting of two approaches (p 75):

• Exact analytical solutions of simplified (approximate) models;
• Approximate numerical solutions of more exacting models.

Both are used in the book.

Near the middle of the book, the author takes up modeling of specific instances of antenna types, starting with open-ended antennae such as the inverted L or radial-loaded monopoles, interspersing interface considerations such as coil loading. Example 6.11 is "A Cordless Phone Antenna." Chapter 7 moves into closed-wire (loop) antennae -- thick loops (doughnuts), barrel loops, cell-phone strap loops, solenoids, the contrawound toroidal helix, and the folded spherical helix monopole. Relative merits of each are included and discussed in a way that shows the author has extensive experience with antenna design, implementation, and testing.

Ferrite rod loop antennae appear in Chapter 8, along with some receiver front-end circuitry. Active antennae are those integrated into the front-end circuitry so as to take into account "the antenna's transfer and reactance characteristics in order to flatten out and broaden the overall transfer from wave field strength to output voltage." Active whips and loops follow.

Chapter 9 takes up the practical topic of measurements. SWR and Z meters are small, battery-powered and cheap nowadays but one must take into account the effect that transmission lines or even standing in the near-field of the antenna will have on measurement accuracy. Use of choke baluns and ferrite toroids keep currents where they are wanted. Old tricks of the trade are conveyed, including some used by radio amateurs.

This book goes a long way in dispelling the mystery surrounding antenna theory for lumped-parameter circuits engineers and EE students. It includes problem sets at the end of each Chapter and can be used as a textbook. I was favorably impressed by this book. In its concentrated coverage of small antennae it also illuminated much else involved in radio communications. For more on it, see http://www.newnespress.com.