LPDA Notes - Volume 2: Hybrid LPDAs
L.B. Cebik, W4RNL

he first book, LPDA Notes, Volume 1 (Pure LPDAs), looked at the basic properties of pure log periodic dipole arrays, with special emphasis upon the types of antennas usually created by radio amateurs. In this companion Volume 2 of LPDA Notes, W4RNL continues his exploration of log periodic dipole arrays, and enters the realm of hybrid LPDAs. This Volume is made up of three main Parts. Part 1 begins with a detailed analysis of the strengths and weaknesses of various traditional designs for the log-cell Yagi, essentially a 2-5 element LPDA with the addition of a parasitic director and reflector. Then, Part 2 turns to the proper long-boom design for such antennas, with the numerous elements, sorting out the effects of the many variables involved in their design. Part 3 explores a number of design considerations for practical LPDAs, including lower HF vs. UHF designs, narrow-band vs. very wide-band designs, and closing with split-band vs. continuous-band designs.

As with all W4RNL books, this volume is extensively illustrated both graphically and with analytical antenna designs. This book contains 200+ pages and 180+ illustrations of diagrams, equations, graphs, patterns, models, etc. and as the title implies, is mainly devoted to hybrid LPDA-Yagi designs, often called “log-cell Yagis,” and often designed for single amateur bands. They, too, deserve some new and systematic attention. In addition, Volume 2 will allow some room to take up additional applications of the LPDA.

LPDA BACKGROUND
The log periodic dipole array or LPDA burst upon the antenna scene in the 1960s as a practical antenna with directional gain and an exceptionally wide (theoretically unlimited) frequency range. Like the Yagi-Uda array, it used linear elements. At the upper HF range and above, the elements might be aluminum tubing or rods. The result would be an antenna that we might rotate in the usual ways that we apply to Yagis. However, we would obtain Yagi performance over frequency spreads of 2:1, 3:1, and higher. Moreover, the entire set of LPDA dimensions could be calculated from a set of engineering equations that assured success due to their precision.

The advent of accurate computer modeling of LPDAs has allowed us to look systematically at LPDA designs, especially those smaller, shorter, sparser versions likely to be used by radio amateurs. Out of such studies have surfaced two benefits:

• One advance has been a better understanding of the properties of LPDAs as we transform calculations into wire and tubular arrays. Earlier studies based on experimental physical models were as thorough as such work could be, but were still limited by the need to check the antenna at selected frequencies. Systematic modeling can increase the number of checkpoints across a frequency range nearly without limit, uncovering unsuspected behaviors along the way. Many of the formerly odd behaviors of LPDAs have become customary expectations, especially of smaller versions. Indeed, we may now catalog the potential limitations of small LPDAs.

• The second advantage that systematic modeling has brought to the study of LPDAs is the development of some curatives for at least the most problematical limitations of LPDAs. Many of these ameliorative measures we must apply to individual designs in doses that vary from one design to the next. Modeling permits the rapid modification of an LPDA design so that it may live up better to expectations — or shows the designer the reason why it needs a replacement.

After looking at the limitations of the LPDA design procedure and the process of adequately modeling an LPDA, this Volume 2 along with companion Volume 1, explores these potentials for elevating the performance of small LPDA designs. In the process, the book also uncovers some myths of LPDA and other array designs, including arranging elements in a forward-looking Vee.

Considered an expert on antennas, L. B. has published over a dozen books, with works on antennas for both the beginner and the advanced student. Among his books are a basic tutorial in the use of NEC antenna modeling software and compilations of his many shorter pieces. His articles have appeared in virtually every amateur radio publication, with translations of some into several languages. Retired Professor from the University of Tennessee at Knoxville, LB is Technical & Educational Advisor to the ARRL.

SOFTCOVER OR PDF VERSIONS AVAILABLE ~ CD OR DOWNLOAD
We offer a special discount price for purchase of BOTH of the 2-Volumes for either softcover or PDF versions. This is a savings of 20% off the normal purchase of each volume separately.

This book is available in softcover or PDF versions. The eBook may be purchased by download directly from this website, or shipped on CD-ROM. You may order your choice of softcover or eBook directly online from our Secure Website, or by FAX, telephone or postal service. Links to the ORDER FORMS with all ordering information are provided here.

Book Versions	Catalog # Vol 2	Regular Price	Catalog # Vol 1 & 2	Both Volumes
SOFTCOVER BOOK ORDER FORM	LBSC-005	$29.95 USD	LBSC-006	$47.95 USD
eBOOK CD-ROM ORDER FORM	LBOD-005	$24.95 USD	LBOD-006	$39.95 USD
eBOOK DOWNLOAD ORDER FORM	LBDL-005	$22.95 USD	LBDL-006	$36.75 USD