Two
Element Horizontal Beams,
Volumes 1 and 2
by L. B. Cebik, W4RNL
Plus 207 Example Antenna Modeling Files,
and design & matching calculators in Quattro Pro & MS Excel-XLS spreadsheets
Volume 1:
Phased Arrays
espite
the high volume of amateur literature on 2-element horizontal beams, most
amateurs do not have a clear set of performance expectations or a general idea
of how they actually work. Cebik has divided the general subject into two parts,
with Volume 1 devoted to phased 2-element arrays. Not all phased arrays, with
both elements supplied energy directly from the source, are (uni-)directional.
In fact, bi-directional arrays have a long service history that is far from
over. After an introduction to phased arrays, the next two chapters give
individual treatment to the famous W8JK flattop array and the equally famous
lazy-H array. Both types of antennas are as serviceable today as they were when
developed in the 1930s and 1940s.
The remaining 7 chapters provide a step-by-step progression ultimately into the
details of phasing two elements to provide an understanding of how these
antennas work and the limits of what they can do. The performance limits emerge
from models with separate sources for each element. In principle, we can design
phased arrays for maximum gain (and very poor front-to-back performance) or for
the maximum possible front-to-back ratio (but modest, though usable forward
gain). Next come the limits of performance that we can obtain from feeding only
one element and developing performance by the geometry of the 2-element array
(as a foreshadowing of the detailed analysis of parasitic beams covered in
Volume 2).. Since most 2-element phased horizontal arrays use transmission lines
to obtain the correct relative current magnitude and phase angle on each
element, Cebik next explores the ZL Special array in several configurations,
followed by the elements of analysis for the current-phasing conditions. More
complex forms of phasing follow, including the HB9CB, the N7CL, and a little
used alternative form involving longer elements. All of these arrays use design
parameters that set them between the two ends of the performance scale set out
in the initial step of the analysis.
The final two chapters cover practical matters, such as extended uses of the
2-element phased array as the driver section of larger beams and the conversion
of uniform-diameter elements used in models into stepped-diameter elements
actually used in the construction of practical HF beams. (Additional
construction suggestions appear in Volume 2, which is devoted to parasitic or
Yagi-Uda 2-element beams.)
The volume illustrates that fact that all 2-element horizontal beams are phased
arrays, whether we feed both elements or only one of them. The first volume in
this 2-volume set contains 217 pages with 170 illustrations and tables. Attached
to the volume is a large collection (92) of EZNEC-format models used in the
study for use by the reader, either to correlate to the text or to serve as the
basis for a practical antenna project.
Volume 2: Parasitic
Arrays
overs
the performance and dimensional parameters of parasitic beams that have evolved
from the initial work of Yagi and Uda in the 1920s. The very first chapter
acquaints the reader with the basic and occasionally confusing language applied
to the various performance categories applied to directional parasitic arrays,
as well as to the fundamental properties of the ½-λ dipole on which the
performance of all 2-element Yagis rests. The next chapter provides an overview
of the performance expectations that we can have from full-sze 2-element
driver-reflector arrays, the most common form of the beam.
Because radio amateurs are always seeking ways to shrink HF Yagis, the next two
chapters examine the performance that we can obtain from various forms of
element shortening techniques. Beginning with element end hats, the treatment
also explores inductive loading in the form of center and mid-element load
positions. It also includes notes on so-called linear loads that in fact are
forms of center inductive loading using shorted transmission line stubs to
produce the required inductive reactance. Part 1 concludes with a survey of
methods used to improve 2-element performance, including the use of
driver-director arrays that sacrifice operating bandwidth for added gain and
front-to-back ratio.
Part 2 of the volume covers the three most common forms of matching the
typically low 2-element Yagi feedpoint impedance to the usual 50-Ω coaxial cable
of most amateur installations. Separate chapters look at the theory and practice
involved in series matching systems, beta or hairpin matching systems, and the
gamma match.
The final part of the volume provides the dimensions and performance details of
very useful 2-element beams for each of the 5 upper-HF amateur bands using
practical stepped-diameter tubing schedules. The chapter on full-size Yagis uses
wide-band driver-reflector designs with a direct 50-Ω feed for each of the three
wider bands. For the 2 narrow bands, the chapter provides similar information on
driver-director designs and beta matches. The final chapter provides
stepped-diameter dimensions for practical Moxon rectangles that save
installation space and provide a 50-Ω feedpoint impedance. Within these final
two chapters are extensive suggestions for applicable construction techniques.
The collection provides the home antenna builder with alternatives to the many
published 2-element designs available.
Like Volume 1, Volume 2 includes a collection of antenna models (115), most in
EZNEC format, that track the antennas discussed in each chapter. The volume has
236 pages, with over 200 illustrations and tables.
The Author
Considered an expert on antennas, L. B. has published 20+ books 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. Retired
Professor from the University of Tennessee, Knoxville, LB is Technical
& Educational Advisor to the ARRL and Technical Editor for antenneX.
Here
is an index of the contents found in VOLUME 1 |
| Chapter |
Title |
Page |
|
• |
Introduction
to 2-Element Arrays |
5 |
| • |
Part I:
Bi-Directional Arrays |
|
| 1 |
The W8JK
"Flat-Top" Array |
28 |
| 2 |
The Lazy-H
Array |
48 |
| • |
Part II:
Directional Arrays |
|
| 3 |
The Limits of
Performance |
71 |
| 4 |
The Limits of
Geometric Phasing |
95 |
| 5 |
The Limits of
a Single Phase Line: The ZL -Special |
115 |
| 6 |
The Analysis
of the ZL-Special |
137 |
| 7 |
Removing the
Limits by Element Matching |
154 |
|
8 |
Extending the
Uses of 2-Element Phased Arrays |
176 |
|
9 |
Converting a
Uniform- to a Stepped-Diameter Model |
200 |
| • |
Other
Publications |
218 |
| |
|
|
Here
is an index of the contents in VOLUME 2 |
| Chapter |
Title |
Page |
|
• |
Introduction
to 2-Element Beams |
5 |
| • |
Part I:
2-Element Parasitic Beams |
|
| 1 |
Methods, Units
of Measure and the Dipole Standard of Reference |
11 |
| 2 |
The Full-Size
2-Element Yagi |
31 |
| 3 |
Shortened
Dipoles and Capacity Hat Yagis |
51 |
| 4 |
Loaded Yagi
Elements |
71 |
| 5 |
Strategies for
Improving Forward and Rearward Performance |
93 |
| • |
Part II:
Beam-Matching |
|
| 6 |
Series
Matching Systems |
115 |
| 7 |
Beta/Hairpin
Matching Systems |
137 |
| 8 |
Gamma Matching
Systems |
153 |
| • |
Part III: Some
Practical HF 2-Element Parasitic Beams |
|
|
9 |
Beams for 20
through 10 Meters |
183 |
|
10 |
Stepped-Diameter Moxon Rectangles |
209 |
| • |
Other
Publications |
237 |
| |
|
|
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