n Volumes 1 and 2 of this series, the author covered the basic theory behind the generation of log periodic dipole arrays (LPDAs) and provided readers with a large number of methods by which to obtain the highest and most consistent gain across a design passband.  The volumes included a wide selection of designs of various sizes to supply the reader with a good sense of LPDA performance capabilities under a range of design values for τ and σ.  The volumes also touched upon numerous design issues, such as the use of thin wire element at lower frequencies, the difficulties of very wide frequency ranges, and others.

Volume 3 of this series takes a broader view of log periodic arrays (LPAs).  Beginning with two further studies into LPDA design factors, the first chapter addresses the role of shorted stubs attached to the center of the longest element, as they function to move the frequency of anomalous frequencies, but fail to remove the anomalous behavior.  A companion study looks into the periodic nature of current maximums and minimums along a set of LPDA elements under varying conditions of phase-line characteristic impedance, element diameter-to-length ratios, and other design factors.

Part 2 of the new volume explores the predecessors to LPDAs, the zig-zag log-periodic arrays consisting of two bays having a constant vertical angle between them.  These arrays took two general forms, using either triangular element or trapezoidal element configurations.  As well, it is possible to build them with or without a central boom interconnecting the elements within each bay.  The notes explore the conditions for optimal gain performance, optimal front-to-back ratio, and the most acceptable pattern shape.  As well, the notes compare zig-zag LPA performance to the performance of corresponding LPDAs.

The third part of these studies looks at the extended aperture LPDA (EALPDA), patented in the 1970s by TCI.  One chapter examines the foundation of extended aperture elements, while another probes more deeply into the patent claim that the EALPDA is equivalent in performance to a standard LPDA, but with a much shorter boom and far fewer elements, since each element has a broader frequency range in LPA performance.  The exploration covers comparative performance models for both EALPDAs and standard LPDAs in various orientations as horizontally and as vertically polarized wide range antennas.

The final part of the volume examines two relatively independent concepts.  One is the use of V-elements in LPDAs, pioneered over 4 decades ago at the University of Illinois, where the basic ideas of LPDA design emerged.  These designs, much misunderstood by the amateur-radio community, show the ability to cover considerable frequency ranges so long as the ranges have a 3:1 ratio.  Their limitation for some proposed application lies in the absence of performance in the frequency region between the two passbands.  The final chapter examines an LPA that is not linear.  It provides a study of a log-spiral LPA designed for lower-HF NVIS service to determine the operating range and performance capabilities of the design in wire form.

Volume 3 of LPDA Notes has no focal conclusion.  The studies extend the scope of notes on log periodic designs and thereby provide a better feel for the place of LPDAs within the total span of log periodic designs and more generally of frequency-independent antenna design.  However, they cannot close the book on these intriguing and useful antenna configurations.

A Potpourri of LPAs contains 208 8.5x11-inch pages, filled with dozens of tables and nearly 200 figures, plus 95 modeling files.

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.

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