Some Basics of
Multi-Band Beam Design
by L. B. Cebik, W4RNL (SK)
(A posthumous publication release by antenneX)

Plus 52 Example Working Antenna Modeling Files

WHAT IS A MULTI-BAND BEAM?? (In the words of LB Cebik)

beam is any directional antenna. In the broadest terms, then, a multi-band beam is any antenna that is directional on more than one amateur band. (Of course, we can make multi-band beams for other than amateur radio use, for example, for the old lower- and higher-frequency television broadcast channels.) We shall pare down our subject by first limiting ourselves to horizontal antennas, the type used in the upper HF and the VHF regions of the spectrum.

There is among some amateur radio beam designers a special art: the art, science, and craft of designing multi-band parasitic beams. Sometimes the work of an individual, sometimes the work of a team, designing directional antennas that cover more than one amateur band is not as easy as it may seem on the surface. We cannot simply interlace a collection of monoband beams, since all of the off-band elements will be active, at least at a low level, on all bands. The interactions are sufficient to complicate the process of deriving on all bands adequate gain, respectable front-to-back ratios, clean radiation patterns, and an acceptable feedpoint impedance. As we shall discover, maneuvers (such as changing element length or spacing) often bring conflicting results. An increase in gain reduces the front-to-back ratio—or vice versa. Peaking the radiation performance play havoc with the SWR curve for one or more bands. The problems increase almost exponentially with the array boom length and the gain that we try to extract on all bands.

The process of designing multi-band beams has largely hidden beneath a veil of silence. Those who pursue this work very often have a proprietary interest in the designs. Some with a virtually intuitive knack for the process very often cannot clearly articulate what they do so well. So most amateur literature simply passes over the subject or presents a design without much theoretical commentary. We, the outsiders who look in on multi-band beam design, view it as a mystery, as a function of secret optimizing software, as esoteric knowledge to which the average amateur is denied access.

Fortunately, enough information as emerged over the last 20 years that we can begin to make some inroads into the task of designing an effective multi-band beam. Part of the information is subject to at least qualitative codification, although we are far from a clear systematic quantitative analysis. We have learned much about the interactions, at least to a level that makes it possible for someone versed in the use of antenna modeling software to begin designing at least rudimentary multi-band antennas. This volume simply presents what I have managed to learn about the process over the years. I have certainly not learned everything—just enough to get started and to realize the limits of what I know. —LB Cebik

Like many of his other books and as explained above, This book includes a collection of 52 antenna models, most in EZNEC format, that track the antennas discussed in each chapter. The volume has 247 pages, with hundreds of illustrations and tables.

For much more information about the contents of this book and why use them, the following link will display a PDF of the book's preface: Click for the Preface

The Author
Considered an expert on antennas, antenneX has published 30+ books by LB Cebik with works on antennas for both the beginner and the advanced student. Among his books are two tutorials in the use of NEC antenna modeling software and compilations of his many shorter pieces and some 800 modeling files, all of which are available here in the Shopping Shack. His articles have appeared in virtually every amateur radio publication, with translations of some into several languages. He is a retired Professor from the University of Tennessee, Knoxville and holds a PhD in Philosophy. Until his death in April 2008, LB was Technical & Educational Advisor to the ARRL and for 10 years was Technical Editor for antenneX. His contribution of articles to antenneX first appeared in early 1997 and a new monthly column, Antenna Modeling, appeared starting in 1999. He is greatly missed, but antenneX is pleased to be able to bring more of LB's contributions to those who seek to learn about the field of antennas.

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