LPDA Notes - Volumes 1, 2 & 3

 

lpda1_ad.jpg (10601 bytes)LPDA Notes - Volume 1: Pure LPDAs
L.B. Cebik, W4RNL

lpda_l.jpg (933 bytes)og periodics number among the least understood antennas within the amateur community. LPDA Notes, Volume 1 (Pure LPDAs), looks at the basic properties of pure log periodic dipole arrays, with special emphasis upon the types of antennas usually created by radio amateurs. The book begins with a review of LPDA theory, modeling constraints, and common properties of LPDA performance. Part 2 explores the small arrays that radio amateurs generally develop, examining their limitations and ways to overcome some of them. The final part of Volume 1 looks at practical LPDA designs that perform effectively throughout the upper HF amateur bands, with some notes on stretching the 20-10-meter range to include 30 meters as well. Volume 2 will examine "impure" log periodics, that is, hybrid LPDA-Yagi designs; it will also introduce further practical LPDA designs for both wider and narrower frequency ranges from 80 meters to UHF.

MORE 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 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.

This first volume of 200+ pages and 170+ illustrations of diagrams, equations, graphs, patterns, models, etc. is largely devoted to “pure” or nearly pure versions of the LPDA. In Volume II, I shall turn attention 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, the second Volume will allow some room to take up additional applications of the LPDA.

Considered an expert on antennas, anteneX has published over 30 books authored by L.B., 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. Also, he was Tech Editor for antenneX.

Here is an index of the chapter titles found in Volume 1

Chapter

Title

  PART 1: LPDA Fundamentals  
1 Introduction 3
2 Modeling the LPDA 17
3 Some Common LPDA Properties 41
  PART 2: Problems of and Cures for Under-performing LPDAs  
4 Exploring LPDA Designs 59
5 Strategies for Improving Basic Designs 89
6 Wire and Vee-Element LPDAs 127
  PART 3: Practical 1-Octave HF LPDAs  
7 A High-Performance, Long-Boom 14-30 MHz LPDA 147
8 A Family of LPDAs for 14-30 MHz 163
9 Stretching the Octave Limit to 1.5 185
10 Unfinished Business 205
     


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lpda2_ad.jpg (11584 bytes)LPDA Notes - Volume 2: Hybrid LPDAs
L.B. Cebik, W4RNL

lpda2_adt.jpg (1114 bytes)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.

Here is an index of the chapter titles found in Volume 2

Chapter

Title

  PART 1: Log-Cell Yagis  
1 Log-Cell Yagis and Some Standards of Comparison 3
2 Element Phasing and Log-Cell Design 19
3 Some Practical Log-Cell Yagi Designs 35
4 Vee-ing the Log-Cell Yagi Elements 51
  PART 2: Long-Boom Log-Cell Yagi Design  
5 The Fundamentals of Long-Boom Log-Cell Yagi Design 63
6 Design Variables and Relevant Comparisons 79
  PART 3: Practical LPDA Design Considerations  
7 Ham-Band vs. Ham-Band-Plus LPDAs 101
8 Wire LPDAs for 80 Meter 121
9 Wide-Band vs. Narrow-Band LPDA Strategies for HF 145
10 A 3.5-Octave VHF-UHF LPDA 169
11 Split-Band LPDAs 183
12 Epi-Log 203
     


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ad_lpda3.jpg (11584 bytes)LPDA Notes - Volume 3: A Potpourri of LPAs
L.B. Cebik, W4RNL

i.jpg (1114 bytes)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.

Here is an index of the chapter titles found in Volume 3
NOTE: When compared to Vol 1 & 2, the much larger page size used here,
Volume 3 would exceed 300 pages of content vs 192 shown.

Chapter

Title

  PART 1: Further Studies of LPDAs  
1 Some Notes on LPDA Stubs 11
2 Appreciating Current Trends in LPDAs 23
  PART 2: Some Notes on LPDA Stubs  
 3 Preliminaries and LPDAs  42
4 The Trapezoidal Zig-Zag LPA 58
5 The X or Saw Tooth Zig-Zag LPA 75
6 Zig-Zag LPA Data Appendix 95
  PART 3: The Extended-Aperture LPDA  
7 The Extended Element and the Standard LPDA 140
8 The Extended-Aperture LPDA 154
  PART 4: Other Frequency-Independent Designs  
9 The V-Dipole LPDA 171
10 A NVIS-ALE Log-Spiral Antenna for 2.5-12+ MHz 192
     


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