Just the Fractals, Please!

INTRODUCTION
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e have yet another creative device to tell you about in this month’s issue along with many other fine subjects covered by our writing team. While it’s not based on a new concept, it may be “bending wires” in some new way to enhance the ratio of performance-to-volume (“PTV” = new term in the compact antenna vernacular). Designer, engineer and author, Werner Hödlmayr, DL6NDJ presents the findings and results in his article “Fractal Antennas” following several months of research and numerous “cut ‘n try” experiments—and testing. Werner is an active member of the GARDS.

Werner developed several versions of his design based on his research. The first version appears on this month’s front cover of issue #81. As I have done on occasions, I shared a preview of this front cover containing that version of Werner’s. I was then pleasantly surprised by the spirited discussion on our antenna discussion mail list, even though not a single word of Werner’s article had yet to be published.

IS IT A FRACTAL?
The first debates centered on whether the device was truly a fractal. Others said they had tried the fractal concept and saw no useful results to inspire more experiments. Later, it was concluded that the fractal could not possibly contribute any enhancement for better PTV as a compact candidate—all derived from the front cover picture, which is not the "FRACTENT" version that evolved from the one in the picture.

I was very impressed, as always, with Werner's workmanship. It wasn't long ago that Werner presented his version of the "TeslaVert" which has since evolved into TeslaVert X3 and that one was presented in the May 2003 issue, now in Archive VI.

Of course, none of the debates altered Werner’s personal view of his findings and feels much more will be revealed once the 18-page article is published. With his experiments out in the open, he welcomes any and all challenges to his theory about this way of bending wires—then, let the real debates begin—is it a fractal and does it qualify as a compact with good PTV? If so, how good? What kinds of testing has been done and what were the results? What is the advantage of a "tent" fractal design? ...etcetera, etcetera.

DISCUSSIONS
For one, I am always pleased to see new directions explored so that our research doesn’t fall into a rut and progress is stagnated. Even if you don’t have a subscription to our reading rooms filled with technology, you can still join the antenna discussion list and read and perhaps participate in the discussions about such things. The discussion list is not only about new concepts though. It is a valuable source of knowledge with some of the finest and brightest minds in the field—and those with a thirst for knowledge. Just about any question posted, whether about a concept or merely how to best ground an antenna, will receive prompt, polite helpful answers.

A LIKEABLE THREAD
Last month, as one example of the “fun” and the learning experience enjoyed on the antenna discussion list, I picked a single thread about “radiation” that I chose as the "thread of the month." I felt some of these threads were too interesting and important not to share. Considering that the lists only contains about 1,200 subscribers yet, there are some 40-50,000 more of our regular visitors who have not seen the threads. Thus, each month, I will try to bring to your attention another Thread of the Month. Of course, you are encouraged to join the list and read them first hand as my personal choice may not be the same as yours because my choice is also meant to equally cover some of the variety seen there.

Although the thread is from an open forum, I only use Initials or abbreviations of the persons in the exchanges, except for myself). Only very minor edits are made. I will not use quotes from private exchanges which are not contained in the open forum. Those who joined the discussion lists or the archives will recognize these, but there are many thousands more who have not joined up yet and have missed a valuable resource. I hope you enjoy my selection as much as I did.

Last month, I picked a thread about the behavior of radiation on an antenna. This month, I have chosen a good one about modeling—essentially a debate of the pros and cons of how useful simulations are vs. physical experiments. Note: The entire thread has not been repeated here, only the salient exchanges, plus the thread may continue beyond this date of writing:

**THREAD OF THE MONTH**
From: DJJ Dear List, I've just updated my page on antennas to reflect my latest thoughts on the "case-by-case analysis" of considering whether antenna models are sound, and the simulations which use them are trustworthy. The quote here is from an email and my comments on it are below. QUOTE: I am concerned at the increasing reliance of simulation in teaching electronics, in evaluating military strategy, and in many other walks of life. Antenna performance forecasting seems to me to be a microcosm that illuminates these issues. DJJ comments: Many people now have access to software which accurately simulates antenna behavior. To do this it is necessary to construct a model. The process of "modeling" is critical to this enterprise as the simulation has limitations of accuracy depending on the kind of model chosen. In itself, the software is essentially accurate and useful. However, the results it returns, for simulation of real antennas, depends critically on what is built into the model. It is not usually possible, in the NEC2 and MININEC and NEC4 software, to add in all the local effects which will affect the results. This is not just because it is too difficult; there are difficulties in principle, knowing the correct dielectric and conductivity parameters to put in for a real-world installation. Details of the feed arrangement are also difficult to get right. So it is often difficult to know if the results from the simulation of the model represent the real behavior of the antenna it was intended to investigate. The process of running the software always returns a result, and the internal checks on validity, while possible, are subtle. Belief in the results often dissolves into a matter of opinion or faith. This can be the subject of strongly-held views, which can only be resolved by recourse to measurements. Thus, simulation should be regarded (taking the most cautious view) as merely a rough guide to an antenna's behavior in a real installation. Any modeling process needs careful validation by measurements. One is then presented with the choice of which to believe, if there is disagreement. I have seen people worry about 1/10 dB in gain in a simulation. This is probably unsound, and one wonders how many hundreds of hours people spend (no doubt happily) in this kind of activity. However, an anonymous committed modeling expert tempers the remarks above with the following comment. QUOTE: Depending upon the conditions of use and application, NEC can be quite accurate. Under some conditions of application, accuracy deviation of dimensions has run to well under 1% in some design projects. In others, accuracy of construction guidance can be considerably off. The real question is this: what are the conditions for each kind of case? However, that question requires an application-by-application analysis, not a wholesale posture toward modeling. DJJ's comment on above quote: Yes, but application-by-application analysis usually requires experimental measurements to be made to validate the models. Considering this comment, what can be said with confidence is that an unvalidated antenna model is not necessarily a good guide to how a practical antenna may behave. One of the thrusts of the complex-systems research reported elsewhere on my web pages is that simulations are only of use if one knows they are going to be accurate before one validates them against measurements. Most people using antenna models are making extrapolations from validated simulations to applications that they believe to be similar. It is the thesis presented here that this method of proceeding is unsafe and unwise in many cases. Happy New Year DJJ
From: Dan DJJ, You must also take into consideration situations where antenna modeling is the only means of getting at a working antenna. Case in point: the new ADRs. The only method of predicting performance is via MOM and this is available on via NEC modeling. You, yourself said that the mathematics behind predicting their performance is beyond common computation. The proof of the pudding is that the antennas work exactly as modeled with a remarkable concordance between model and wire over a large range of frequencies and a large variety of designs. So one may say that, save for NEC, there wouldn't be such an antenna. We may say this even more for the Prismatic and for the Cube. I believe that one has to have a balanced point of view and an open mind. Dan
From: DJJ Dan, You don't remember perhaps that your NEC predictions for the Ps and the ADRs were very precise and specific, but that when I built them and validated them we discover that "almost anything like this" will work, as well as the specific design that you had come up with. What price modeling then? Anyone who had experimented by throwing together and antenna with this general structure would have hit pay dirt. One gets the wrong idea completely from simulating all the time.... DJJ
From Dan: DJ You missed my point entirely. Whether an antenna "wants" to work, as the Prismatic, or whether it is difficult to get to perform is irrelevant. It is clear with the ADR, Prismatic and Cube-family that they could not have arisen from "paper doodling and building". You spent a lot of time trying to figure out how the Ps work - after the fact. I am extremely pleased that the Ps can be made to work in spite of builder's mistakes, dimensional inexactitude and sloppy construction. More power to them. They arose from modeling. If they are so easy to construct and get to work then why didn't some antenna designer do it first? It may be possible for an antenna designing physicist or engineer to come up with any of these designs from first principles - provided they have the imagination and can "think out of the box" (or "in the box" in the case of the Cubes). But this is not very likely and besides their time is valuable. It is much easier for an amateur or non-professional like me to do so since my time isn't money and I can afford endless hours doing endless mental doodling with models and trial and error. No professional is going to do that. For every design that works there are probably hundreds that don't. It is less of a waste of time to make models than build antennas. Now this, of course, is a scenario where antennas can be modeled in the first place by various programs running into multi-K $. There are antennas out there that cannot be modeled by any means. I am sorry if that is the case because - the bottom line - modeling certainly saves time. As long as we all agree that modeling is but the first step - a guide to building and measuring and validating - we are on the right track. Think of it as a troika - all the horses pulling together else the wagon tips over. Dan
From: DJJ Dan, I don't think you understood my point. I said, "nothing wrong with validated simulations." If they "work exactly as modeled" that is empirical validation. What I object to is prediction without validation. --regards DJJ
From CR: Dan, I agree with DJJ and let me add that for the reasons I gave in the message about the accuracies, "work exactly as modeled" makes me always very suspicious because this normally never happens to me ....and doesn't seems to happens also to the USA National Bureau of Standards .... Kind regards, CR
From: LB Antenna (or more generally, RF or EM) modeling software offers many opportunities, but as well a host of limitations. Suitable caution and NEC model validation for specific applications is, almost without saying, necessary when moving from a general model of some kind of antenna into preparations for seeing if it actually works. Prototype-type construction and measurement of performance are always necessary steps in that process. I tend to grade models that are constructed well within known NEC limits in several levels: 1. suggestive models, 2. proof-of-principle models, 3. general models (that may require re-modeling before they are ready for prototyping-typing), and 4. specific designs. Models such as the automated design model for Moxon rectangles--expected to be operated free and clear of environmental factors--are an example of category 4., and such models have been validated by many successful iterations. General models, category 3, include but are not limited to such antennas as HF Yagis modeled using uniform diameter elements as a precursor to designs using element taper schedules or as a precursor to designing a matching network for the driver feedpoint. Proof-of-principle models include "physical" (GW or wire-based) models of antennas using a gamma match, since such a model would require in NEC that all parts of the gamma match use the same diameter material to avoid a known NEC limitation with angular junctions of dissimilar diameter wires. Hence, the final dimensions would not be suitable for construction of even a prototype, since the gamma match material diameter would necessarily affect other dimensions. Suggestive models, category 1, are those that can only capture some features of an antenna and that may be open to questions--which the modeler should be the first to pose. As I have often noted, all models should be subjected to both the convergence and the average gain tests of adequacy. However, these tests must also be understood as necessary, but not sufficient, conditions of model adequacy. Hence, passing these tests will not ensure that a prototype constructed from the model will measure out as the software reports. There are two seemingly separate sets of limitations when moving from a model all by itself to an application: software limitations and environmental limitations. Small-antenna designers/experimenters routinely press one set of NEC limits, normally the element diameter vs. radius question, not to mention the total wire-length question. However, there are other, sometimes overlooked questions. For example, many models routinely omit parts of the physical structure of any application of the antenna under question. Consider a 1.5 GHz in-phase-fed pair of dipoles in front of a planar reflector. The phase lines represent a significant portion of the structure at this frequency and may or may not reveal interactions with the system such that we see altered performance relative to a model that omits them. On the environmental side, there are critical performance anticipation issues that many modelers overlook. Terrain nature, such as slopes, etc., will alter HF antenna performance, although there are some terrain packages that can accept NEC outputs and give some guidance. There are issues with surrounding objects which may range from buildings to seasonally varying growing stuff to people. To a degrees, models in NEC can capture some of this by modeling the structures with the antenna, but only to a very limited degree. Capturing a tree's structure and conductivity is no mean feat. Buildings often show up only as outlines and may not show the critical conductive portions, such as wiring and ducting. The two arenas intermix. I once encountered a model of the steel framework of a building below a rooftop BC antenna. Using NEC-4, the modeler had modeled the several levels of parking garage below surface grade. However, the real parking garage was open, while the model necessarily filled the garage with soil of the same type as existed beyond the building's perimeter. How many folks glibly model and teach by modeling without constant attention to the interface between models and reality, including appropriate test measurements, I cannot say. NEC has a large class of validated models relative to use in applications that do not introduce extraneous factors. It also has a large class of invalidated models that fall outside the limits of the software. Only users can evaluate the intermixing of environmental factors. Setting up a large model of a modern destroyer for antenna placement modeling is a far simpler task than trying the same task with a W.W.II destroyer (almost the difference between modeling an armadillo and a porcupine). As a vehicle to illustrate basic or even advanced but well-known principles, modeling software can be very fruitful. However, for advanced design work (such as engineering work within a graduate school), limitations and testing become dominant over simple illustrations of known principles. However, and this is the "unfortunately more" part, current emphasis upon the GHz+ range introduces needs that exceed what NEC can give, for example, in the routine use of substrates to support antenna structures, etc. So, for this work, there are a variety of proprietary hybrid packages that combine NEC's MoM algorithms with other techniques (such as but not limited to UTD, FDTD, etc.). While these packages offer ways to account for many things that NEC alone cannot handle, they necessarily have a much smaller list of validated results. As well, for any package, one may have only the maker's certifications of the list of validated models (in contrast to the widely publicized array of both valid and invalid models emerging from NEC). Like hybrid tea roses, nursery claims and garden performance may differ. Because these programs generally come with a high initial cost and a very significant annual "subscription" fee, the programs may change quickly enough that developing a list of validated models may prove almost impossible. Here, the potential user has much less to go on when deciding to invest than with NEC. But, if one cannot do a design task for an application within NEC but--in principle--can with a hybrid, then it is likely that some investment will be made. How good the investment is relative to anticipated applications only the lab will eventually tell--long after it is to late to request a refund. What ties NEC to the hybrids is not NEC, although it may play some role in the package. Essentially both NEC and the hybrids are calculating engines. To effectively use the software in critical situations and applications requires the user to examine and to be conversant with the calculations going on within the engine. NEC is well-established enough that there are guidelines that will keep beginning modelers--those who do not yet grasp the mathematical underpinnings of the engine--out of trouble, that is, well away from the software's limitations. Except where the results of hybrids overlap well-established NEC results, we cannot say the same for these advanced packages. If we only need results that coincide with those of NEC, then one might as well use NEC and save the considerable investment. However, the main uses of these packages is for problems that NEC cannot solve, and precisely here we enter a domain where validation is scant. In fact, precisely here lies the need to present virtually every result to the lab for measurement, since each user with a different intended application will be adding either to the list of validated models or to the list of those beyond the hybrid software limits. If you do work in areas that require constant correlation of lab measurements to software reports, please be certain that the lab meets all current standards for the work, frequency, conditions involved so that the measurements do not become the outstanding question for evaluation. Obtaining valid measurement results may be as much or more an art and science as obtaining a valid and helpful model via software. -73- LB

For those of you who use modeling programs, these subjects come up often on the lists, more so though as results of modeling some project. The more spirited debates of course come from those who had rather build, cut 'n try versus those who prefer to be pure simulators and never the twain shall meet. It really all depends on the purpose of each of these "religions." If each are only for "fun" and are hobbies, there really is no valid reason to disagree with either belief. However, if the purpose of either approach is for that of validation of a certain concept or design for practical application, then the difference in beliefs are of significance, IMHO, to wit:

FOR MORE SERIOUS PURPOSES
Let's look at it this way for a moment: Simulations actually start in the most basic of computers—the mind. A "concept or design" begins as a single kernel of a "thought" that resides within one's mind and that kernel is most likely yet in a crude state and not fully baked. So, does it make sense to take that crude design in mind directly to the workshop and start bending and cutting wires or some other types of materials, plus assembly, plus installing on the roof or mast, plus determining what happens if fed in an almost endless set of assumptions? OR, does it make more sense to take that crude idea and transfer it into some of the powerful software available to us today and then do all of the same things one would have done in the workshop and probably much more?

Of course, the mind can only carry the calculations so far before a decision is reached to go the next step of "cut 'n try" or computer simulation. But, let's not stop here either. Even though the choice may be to choose computer simulation as the next step from the intellectual conception from the mind, eventually, one must go to the workshop and build—and make real test measurements. However, an advantage of the computer approach is that dozens, maybe hundreds of computerized "cut 'n tries" may have been simulated to eliminate most of the most obvious "duds" that would take months or even years to do physically only to discard—and at a much greater cost of time and materials.

Needless to say though, one must master the software and be thorough about the parameter inputs to produce a good representation of the computer model as compared to what will become a physical manifestation. If for a fixed location, one should really be able to refine the design to "fit" the targeted locale like a glove.

Signal patterns. This is another advantage derived from the modeling software. It can even be described as fun to watch how the pattern's shape should appear starting from that first crude design and how the shape changes with each modification to the design (or does not change). One can keep trying modifications until the pattern is the one desired. Now, one has the remaining option of deciding whether it is a practical design—then build it! Now, compare it to the computer model. If it is the same, great, but if not the same, look at what parameter was overlooked.

The real satisfaction comes from eventually seeing that original "kernel of thought" come to fruition and produce the results hoped for—whether via simulation or otherwise!

AN INVITATION TO CONTRIBUTORS
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antenneX thrives on the contributions of antenna experimenters, ranging from the informal home shop construction project to the theoretical investigation of basic antenna, feedline, and propagation phenomena. Over the years, we have published articles on the use of new or newly adapted materials, known antennas adapted to new circumstances, modifications of antenna structures, basic explorations of both common and unusual antennas, antenna modeling exercises, design improvements, antenna matching techniques from both a physical and mathematical perspective, evaluations of mini-antennas and their underlying theory of operation, new and patentable designs, propagation tutorials, and.... The list goes on, since no antenna-related topic is irrelevant to the readers of antenneX.

At the same time, antenneX has experienced continuous growth in its readership—for which we are appreciative. However, all readers can help us do even better. How? By submitting an article every now and then based on your current antenna work that may be useful at any level to other readers.

Among the engineering and researching readers, there are undoubtedly a number of unclassified and non-proprietary findings that antenneX readers would like to know. Among the practical antenna designers, there are ideas, tests, and numerous other practical findings to benefit our readers. Antenna builders very likely have some techniques to share with other readers. Besides the regular articles, we always have the home work shop column for shorter practical ideas and we always have the invited news and editorial column for information about new technologies, future advances, lost old but good ideas, and personal views on the good to bad things that are happening in the world of antennas and propagation.

If you are uncertain about whether your ideas merit an article, please feel free to send an outline to the general editor/publishers at submissions@antennex.com . Do not feel that you must be ready to be a regular submitter to write for antenneX, because we welcome the individual contribution as much as monthly articles. As well, do not believe that the slots in each issue are already spoken for—we shall always make room for a worthy article.

ONE MORE COUNTRY JOINED LAST MONTH!
Country number 187 just joined the listing of "Where in the World is antenneX?" As is our custom, we welcome the latest newcomers and try to tell a little about the countries, some of the history and any other things our research discovers that might be of interest. The US CIA's World Factbook is most helpful in this research. A warm welcome to these latest newcomers!

WELCOME Bhutan, COUNTRY #187
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The Kingdom of Bhutan is geographically located in Southern Asia, between China and India at the coordinates of 27 30 N, 90 30 E. For the USA readers, it is about half the size of the State of Indiana.

Bhutan has a population of just over 2.1 million with only about 4% reaching age 65 or more. Average life expectancy is only about 53. This is the only countries I remember where the male lives slightly longer than female. I have found it more common that females live about 2 years longer in most other parts of the world.

In 1865, Britain and Bhutan signed the Treaty of Sinchulu, under which Bhutan would receive an annual subsidy in exchange for ceding some border land. Under British influence, a monarchy was set up in 1907; three years later, a treaty was signed whereby the British agreed not to interfere in Bhutanese internal affairs and Bhutan allowed Britain to direct its foreign affairs. This role was assumed by independent India after 1947. Two years later, a formal Indo-Bhutanese accord returned the areas of Bhutan annexed by the British, formalized the annual subsidies the country received, and defined India's responsibilities in defense and foreign relations. A refugee issue of some 100,000 Bhutanese in Nepal remains unresolved; 90% of the refugees are housed in seven United Nations Office of the High Commissioner for Refugees (UNHCR) camps. Maoist Assamese separatists from India, who have established themselves in the southeast portion of Bhutan, have drawn Indian cross-border incursions.

Bhutan has no written constitution or bill of rights. The King commissioned a committee to draft a constitution in 2001, but has yet to be approved. Their legal system is based on Indian law and English common law. On village-level elections, each family has one vote.

The economy, one of the world's smallest and least developed, is based on agriculture and forestry, providing the main livelihood for more than 90% of the population.

Communications:
Telephones: About 6,000 lines in use. No mobile or cellular as of last survey (1997).
Radio broadcast stations: AM 0, FM 1, short-wave 1 (1998)
Television broadcast stations: 0 (1997)
Internet country code: .bt
Internet Service Providers (ISPs): NA
Internet users: 2,500 (2002)

Notes on the Batwing
Part 1: Basic Batwing Properties
By L.B. Cebik, W4RNL

Ever on the lookout for wide-band antennas, LB was pleased when John Magliacane, KD2BD, called attention to the "batwing." Long used in a turnstile and phased-vertical-array configuration, the basic batwing is little understood among amateurs and hence, little used. Perhaps it deserves a better fate. This series will consist of 3 sessions. The first will examine the basic properties of the batwing as a very broadband dipole antenna. The second will examine two major applications of the batwing. The final section of these notes will deal with a few modeling issues.

Lab Notes: Rotating Connected Loops
By Joel C. Hungerford, KB1EGI

During the past two months Joel investigated the effect of changing the surface area of a magnetic loop, while holding all other parameters constant and investigated the effect of changing the circumference of one or more parallel connected loops without changing the planes or tuning capacitance. This month Joel looks at the effect of rotating the plane of one of two parallel connected loops through 90 degrees relative to the other loop without changing any other parameter.

Transformer Magnetic Coupling & Matching with One Variable
By Fred M. Griffee, N4FG (EE Retired)

Magnetic transformer coupling and impedance matching have been popular among amateur radio enthusiasts for a very long time. But designing the network has used what might be termed infinite variables used to simplify the design. All this includes is an air core or toroid inductor, with as many coil turn taps as possible on both the primary and secondary, along with a switch to select the best ones, and variable capacitors at the input and output of the transformer for tuning. A different approach addresses Fred's particular antenna system and a specifically designed transformer for each band of interest.

THE "ANTAP" Apartment Antenna: Part II
By Claudio Re, I1RFQ

There is a big demand in the USA for an HF Apartment-sized Antenna that could continuously tune in the range of frequencies from 3-30 MHz. Local and regional regulations often prohibit the use of exterior antennas. Many of the dwellings are built with wood, which is a not a bad insulating material when dry. Many homes have in the highest part of the house as an apartment or an attic where Hams want to put their antennas. However attic apartment space is often limited. This article describes the development of an antenna suitable for this purposes called ANTAP (ANTenna for APartments).

FRACTAL ANTENNAS
By Werner Hödlmayr, DL6NDJ

This article is an overview about fractal geometry in general, and fractal electrodynamics in particular, with applications of this new frontier of science. As a practical example in section 3, a series of 3 fractal antennas are described, that have been built and tested around the center frequency of 145 MHz by using the first and second iteration of a tent transformation. Werner believes the new science of fractal electrodynamics offers very interesting possibilities for designing small, broadband, and efficient antennas for restricted space.

The Compact Cube-C, Part III
The Double-Folded Cube-C
By Dan Handelsman, N2DT and Claudio Re, I1RFQ

This article is the nexus of three separate, but related, trains of thought. The first arises from a modification, developed by Claudio Re of the cube-like Compact Cube-C antenna, which would make it easier to mount on a single central mast.

The second came about because Handelsman became interested in how the position of the “tuning arm” — the extra radiator containing a tuning variable capacitor in parallel with the fed wire — affects the impedance and the radiation patterns of the antenna.

The third arose because of questions by readers of antenneX and the antenna-discussion list. The most frequently asked question was about the need to keep changing the values of Cp the tuning capacitor and Cs the reactance-canceling capacitor with changes in frequency. Handelsman reviewed modeling and experimental data to come up with an encouraging answer.

Well, there you have it, folks—thanks for listening and remember, the reading lamp is always on for you in the reading rooms. If I can be of further help, I'm just a Stone's Throw! away. January 2004 antenneX Online Issue #81
reGARDS, Jack L. Stone, Publisher jack@antennex.com