Age
appears to be the best in four things—old wood best to burn,old wine to drink, old friends to trust, and old authors to read.
—Francis Bacon (1561-1620)
Age
appears to be the best in four things—old wood best to burn,
old wine to drink, old friends to trust, and old authors to read.
—Francis Bacon (1561-1620)
The Archeology of Antennas
By Jack L. Stone, Publisher
INTRODUCTION
he other night I watched an interesting program on the
archeological exploration of an ancient village that was part of a larger
civilization. The narrator did not say whether they had radio and antennas, but the
remnants of clay and stone strongly suggest the negative. I shall very likely forget
much of the detail that I learned about the people and the times. However, the
program contained a number of statements about the modern methods of archeology that
resonated with some of my thoughts about antenna research and experimentation. Those
are the items that I want to write down so that I shall not forget them.
1. All of our present-day efforts build upon the contributions of the past. In archeology, we find a continuous effort to honor the contributors of the past, even though we also have to revise their work and correct their mistakes. Indeed, some of those mistakes become the incentive that spurs new work. The goal is not merely to identify an error and correct it, but also to refit older investigations into contemporary frameworks of understanding. As the art and science of radio communications (in all of its forms) gradually matures, we have gained a new appreciation of the pioneering work that has gone before. That work includes fundamental principles, for which Maxwell’s Laws form a cornerstone. It also includes experimental efforts, some of which rested on only the thinnest of theoretical bases. Marconi had only a smattering of reliable theory underlying his initial broadcasts—a smattering of theory and a very large dose of faith that he was on the right track. The early work also includes engineering feats by Edmond Bruce, John Kraus, and many others who transformed basic ideas into very practical antennas that performed as they predicted. Even academics, such as Yagi and Uda, has a role to play in opening the way to new techniques of antenna design, techniques that eventually became dominant in HF and VHF antenna design. Very often, we can look back to the original work of our antenna forefathers for two important commodities: important ideas we may have previously overlooked and, of course, inspiration.
2. What we bring to our work today is not a set of better minds, but instead a better set of tools and methods. In archeology, we no longer race with grave robbers to loot a site of its artifacts. Instead, we leave the site as open but otherwise undisturbed as possible, treating it as a place of continuing effort. As well, we can now use satellites, subterranean radar, DNA tests, and a host of new tools that not only speed some of the work, but as well amplify the work by opening new roads of investigation. Similarly, in the field of antennas, many of our present tools and methods did not exist in the past. The antennas of the 1920s through the 1970s or 80s rested largely on hand calculation, with some effort to encapsulate those calculations into nomographs for future use. Nevertheless, modern methods can hardly improve on some of the results, for example, in the design of rhombic antennas. In other cases, newer computer methods have finally permitted the perfecting of antenna designs whose performance had languished using only experimental methods. For example, there is a very sudden explosion in the number of Yagi designs beginning about 1990. Almost all of the designs after that date will outperform virtually any design prior to that date. The key has been the development of computerized antenna design and analysis programs. Some of the latest hybrid programs are capable incorporating processing circuitry, matching networks, transmission lines and antennas into a single set of traces and components bonded to a substrate. But, like all tools, the output is only as good as the skill and knowledge of the scientists, craftsmen, and artists who wield them.
3. Everything forms a puzzle into which each piece fits naturally, without forcing. I read a recent article in Scientific American on the history of our system of constellations. The very informative article had a few spots of fungus. The author noted in more than one case that present evidence of X is lacking and so Y must “undoubtedly” be the case. That sort of statement might be fine for well-known fictional English detectives, but it lacks a certain restraint more fitting to modern archeology. Y is not without doubt, but instead only the most plausible of presently known alternatives. The history of antennas is filled with equal attempts to fill in gaps more with force than with the naturalness of proper mathematics or measurement. When the HB9CB and the ZL-Special antennas appeared in the early 1950s, writers attributed to 2-element phased horizontal arrays more gain than 3-element Yagis. Gain estimates of up to 9 dBi (using the modern free-space measure) accompanied articles on these arrays. The force-fit operation consisted of assuming that existing amateur Yagis performed up to their theoretical limit. The superior performance of the newer phased beams “undoubtedly” arose from their higher gain potential. What ensued for decades into the present era of antenna understanding have been attempts to preserve the old force-fit idea with shrouds of very dubious rhetoric. In fact, the amateur HF Yagis of the 1950s had some front-to-back ratio, but very poor gain. With that understanding, at least this part of the antenna puzzle began to fall more naturally into place.
4. Whatever we do today, we record, catalog, and document as fully as possible, and we leave the field of investigation as pristine as circumstances will allow, so that those who come after us can apply their own new tools, their own new methods, and their improve understanding to reach even better conclusions. The field of antenna investigations, of course, has no “dig sites” to leave behind. We must rely upon texts, articles, diagrams, plans, and photographs to gain a feel for the work of the past. The giant fields of western fir supports and vast arrays of wire have given way to antennas that require less acreage to make room for subdivisions and shopping malls. But we do have all kinds of documentation that we can leave behind for the next generation of investigators, whatever the level of their work, from basic theory to practical antenna implementation. Precisely here antenneX and you both have a role to play. antenneX is a vehicle to present antenna ideas at all levels of work for the edification and inspiration of others. The antenneX archives provide a long-term storage vehicle for these ideas. The antenneX Archive users look back to the earliest issues as much as they examine more recent work.
The final ingredient is you, the antenna investigator and experimenter. Your best work deserves preservation in quality antenneX articles. We cannot say in advance that a given piece of work will either endure as a new cornerstone for others or become the basis for a new correction. Either way, it becomes a part of the documentation that will be of service to coming generations of new antenna experimenters. Keep on keeping on!
A PRESS RELEASE
Announcing A Continuing Education Course on: ANTENNAS AND
PROPAGATION - 20-24 November 2006
If you live in the UK, have plans to visit the UK in late November 2006, or need a good
reason to go, you might want to consider the short course on Antennas and Propagation
being offered by the University of Surrey Guildford, Surrey.
Some of our readers have taken previous such courses and have reported to have really
enjoyed them. Below is more info. If interested, contact Barbara Steel as shown at the
bottom of the following Press Release.
 School of Electronics and Physical Sciences Announcing A Continuing Education Course on: ANTENNAS AND PROPAGATION The course is designed to provide an overview of the fundamental principles associated with microwave and RF antennas and propagation. The course will present the underlying theory in an accessible manner, together with techniques for application of the theory to satellite and mobile communications scenarios. The course is partly based on a previous MSc module at Surrey University. Topics include antenna principles and calculations from electromagnetic theory; VHF/UHF propagation prediction, and overcoming channel impairments, HF propagation and some antenna demonstrations. The course will suit engineers working in the Antennas industry and related fields. Course Outline: Principles of Antennas 1 and II; Principles of Radio Wave Propagation Effects; Principles of Propagation Effects; Aperture Antennas; Wire Antennas I and II; Transmission Lines and Feeders; Propagation-applications to systems; Mobile Systems design; HF Ionospheric propagation; Stub matching, Smith chart details; Array antennas; Printed and Mobile Antennas; LABS including X band antenna demonstrations, knife edge diffraction, polarisation on reflection, antenna gain and beamwidth measurements; LABS including Introduction to NEC simulations, demonstration of slow wave structure antennas (Zagi, Fishbone); LABS including Demonstration of small tuned loops and log periodic antenna, and microwave can antenna. |
THE COURSE The course is designed to provide an overview of the fundamental principles associated with microwave and RF antennas and propagation. The course will present the underlying theory in an accessible manner, together with techniques for application of the theory to satellite and mobile communications scenarios. The course is partly based on a previous MSc module at Surrey University. Topics include antenna principles and calculations from electromagnetic theory; VHF/UHF propagation prediction, and overcoming channel impairments, HF propagation and some antenna demonstrations. It is recommended that, if an attendee has less than a years experience in Antennas and Propagation, that they look at David Jefferies comprehensive website prior to the course which can be found at the following address:- http://www.ee.surrey.ac.uk/Personal/D.Jefferies/teaching.html LECTURERS Professor Mike Underhill MA, PhD, FEng, FIEE, FRSA joined the University in 1991 and was formerly Head of the Applied Electronics Research Group and Dean of Engineering. Previously, he worked for Philips Research Laboratories then as Technical Director for MEL-Philips and for Thorn EMI Sensors as Engineering Director. He has been involved in Defense Electronics (mainly H F Radio) since 1961 and EW and Radar and IR since 1980. His current research interests include low phase noise in oscillators and frequency synthesis, low jitter clocks and clock recovery, HF transmitting loops and associated electromagnetic theory, millimetric and satellite borne HF radar and Ionospheric sounding. He holds about 50 patents in these and related fields and has published about sixty papers. He has been a Fellow of the Royal Academy of Engineering since 1993. Dr David Jefferies MA, PhD, MIEE, MInstP, C.Eng, C.Phys, is an experienced lecturer, a member of the Institute of Physics and the IEE. He is also a former editor of the International Journal of Electronics and has worked for Oxford, Stanford, Aberdeen and Nottingham Universities. In the 1980s he ran the Oxford Physics Laboratory’s electronics option course and researched non-linear properties of ferroelectrics. His current research interests include:- chaos in electronic circuits, complex systems and parallel non-deterministic computation and has published many papers in these subjects. Dr Mike Willis PhD University of Surrey, BSc University College London. Currently Head of Radio Research at the Radio Communications Research unit of the Rutherford-Appleton laboratory, mainly working on projects aimed at promoting more efficient use of the radio spectrum for the UK regulator Ofcom. He is Chairman of the IET task Group on Mobile and Terrestrial Propagation. He actively participates in the ITU-R Study Group 3 improving existing and developing new recommendations on radio wave propagation. His PhD focused on fade countermeasures for VSAT services employing the higher frequency bands above 20GHz. DETAILED SYLLABUS (please note that the University of Surrey reserves the right to update and alter these courses – please check our website for updates) Principles of Antennas I and II Dr David Jefferies Electric and magnetic fields, and relations between them. Maxwell’s equations. Poynting Vector. Plane waves, impedance, velocity. Boundary conditions. Conductors and dielectrics. Categories of Antenna, lists of types, examples. Aperture antennas Transmission lines, traveling and standing waves. Doublets and Dipoles Field calculations from known current distributions. Radiation patterns. Isotropic radiator. Definitions of gain, radiation resistance, effective aperture. Matching and maximum power transfer. Near and far field regions. Broadband antennas – prismatic polyhedron. Antenna size reduction – Zagi, fishbone, slow wave structures. Narrowband antennas, short dipoles, small loops. Principles of Radio wave Propagation Effects (Parts 1, 2) – Dr Mike Willis
Propagation in free space. Plane waves; Field strength against distance; Some examples – Voyager (in brief);
Line of sight propagation through the atmosphere:-Free Space Loss; Atmosphere with height; Refractive index of air; N – units; Water vapour vs height; 4/3 Earth approximation; Inversions; Ducting; Scintillation; Gaseous Absorption; Rain/Hydrometeors; Rain rate, example maps; on-uniformity over an area
Non line of sight propagation effects; what is line of sight; the path profile; Fresnell Zones. Diffraction: - Knife edge diffraction. Models for multiple knife edges:- Vogler; Deygout; Giovanelli; Reflection/Scattering. Surface roughness:-Phase changes; Horizontal vs Vertical polarisation; Reflection/scattering from real objects; Rayleigh/Mie scattering.
The concept of channel variability over time:- Introduction to PDFs/CDFs and their use. Example of rain rate; Extension to specific attenuation; other things that vary - temperature, humidity, pressure, clutter (vegetation, buildings), Ionosphere TEC (GPS errors), terminal location
Principles of Propagation Effects (Part 3) – Dr Mike Willis
Channel characteristics, Ideal vs reality and variation with frequency:- Fast Fading; Rayleigh/Rician formulation; Slow fading; Coherence; Multiple paths; Delay & delay spread; Doppler & Doppler spread; Examples for Terrestrial Channels; Satellite channels; Mobile Channels; Link budget calculations; The signal power at the receiver; The noise at the receiver; Boltzmann's constant; Background noise temperature; Calculating the antenna noise temperature. Channel measurements:- Need for channel modelling; Who produces models and where to find them; The types of models; Site specific, Site general, Statistical Testing models against measurements; mean error, standard deviation, testing variables.
Aperture Antennas - Dr David Jefferies
Reflector antennas, Casegrain, Gregorian, Offset. Ray optical design. Diffraction theory for far field polar pattern. Gain and pointing accuracy. Rigidity, blockage, profile errors. Noise temperature and effects of rain. Ground station considerations - target tracking. Optics. Feed geometry. Cross polar performance. Satellite antennas - beam forming techniques using multiple feeds. Shaped reflectors. Multi frequency systems. Performance parameters from a systems point of view. Antenna measurements - Pattern, gain, and cross polar measurements. Terrestrial ranges. Near field measurements. Extra-terrestrial source measurements. Noise temperature measurements. Wire Antennas I and II – Professor Mike Underhill
Hertzian dipole. Half wave dipole. Folded dipole. Baluns. Resonant and non-resonant antennas. Antenna matching. Arrays, Yagi-Uda, broadside. Rhombic, helical. Mobile Station Antennas: - Monopole. Loading with capacitance and inductance. Loops, Helicals. Planar inverted F antennas. Base Station Antennas: - Vertical gain. Collinear. Sector antennas. Corner reflectors. Printed arrays. Transmission Lines and Feeders – Dr David Jefferies
Simple wave propagation on transmission lines. Reflection coefficient, SMITH chart, network analyser, balanced and unbalanced transmission, lossy transmission lines, horn feeds, apodisation, power handling. Propagation - applications to systems – Dr Mike Willis
Terrestrial fixed systems. Terrestrial line of sight systems; LOS Propagation effects & appropriate models for each; Reminder about system availability; FSL; Multipath & dispersion; Diversity antennas; Rain specific attenuation; Gaseous attenuation. Trans-horizon effects; Path profiles; Refraction/Ducting; Diffraction (Deygout, and similar models); Troposcatter; Rainscatter; ITU-R P.530, P.526, P.452; Interference calculations; Example 1 – microwave link, Example 2 – Troposcatter system
Extension to Point to Area systems (broadcast, WiMAX); VHF/UHF broadcasting; Models based on curves e.g. ITU-R P.1546; Coverage vs building blockage propagation into buildings, propagation within buildings. Example – a WiMAX deployment
Propagation-applications to systems – Dr Mike Willis
Fixed Satellite systems; The particular issues due to slant path. The atmosphere; Rain fading along slant path, Models for rain rate, Path reduction factor, Fade mitigation, Scintillation. The Ionosphere; Faraday rotation; Path length and GPS; ITU-R models. Sharing issues; Fixed links vs satellite earth stations. Example 1 – Geostationary satellite link, Example 2 – Space probes (Deep Space Network, UoSAT).
Mobile Systems design – Dr Mike Willis
What is unique to mobile systems:- Movement; Antenna; Location deep within clutter (no mast); Availability; Private Business Radio; coverage; shared channels - blockage probability. Mobile phone systems:- Cell types, Macrocell, microcell, picocell; Satellite mobile; Path Loss mechanisms; Free space, Shadowing, Vegetation, Multipath. Aside – MIMO Channels, Path Loss models. Empirical: Power law, Clutter factor, Okumura/Hata, COST-231 Walfisch-Ikegami. Theoretical: Multiple Building Diffraction, Ray tracing. Comparison of theoretical and empirical models. Statistics & models for: Shadowing, Delay spread, Location variability.
LF and MF broadcast antennas - Professor Mike Underhill
Ground-wave propagation. Ground and environmental losses. Environmental Noise. Definitions of Antenna Efficiency and Effectiveness. Verticals, Ground Planes. Anti-fading antennas.
HF Ionospheric propagation – Professor Mike Underhill
Ionosphere, description and properties. Maximum useable frequency, sunspot cycle, ducting, examples of round-the world echoes.
Stub matching, Smith chart details – Dr David Jefferies
Antenna matching methods; bandwidth, resonant stub matching, SMITH chart calculations, examples of SMITH chart plots of real antennas, derivation of return loss and bandwidth, SMITH chart as admittance plot; series and shunt stubs; open and short stubs; quarter wave transformers; broadbanding techniques.
Array antennas – Professor Mike Underhill
Definitions, array factor, element factor, pattern multiplication, pattern examples, recursive array antenna design. Null placement.
Printed and Mobile Antennas – Professor Mike Underhill Microstrip discontinuities and patch radiators, surface waves and transitions, feed types, basic design methods, notion of CAD, innovative arrays and integrated antenna concepts. Mobile handset antenna requirements, fundamental properties of electrically small antennas, size reduction techniques, handset health considerations, satcom handset antennas. LABS - Dr David Jefferies and Dr Mike Willis
X band antenna demonstrations, knife edge diffraction, polarisation on reflection, antenna gain and beamwidth measurements
LABS – Dr David Jefferies Introduction to NEC simulations, demonstration of slow wave structure antennas (Zagi, Fishbone)
LABS – Professor Mike Underhill Demonstration of small tuned loops and log periodic antenna, and microwave can antenna.
Further details can be obtained from the University's website at: CONTACT: |
THE PURPOSE OF THIS JOURNAL
In my column for September 2006, “The antenneX Mission,” I wrote about
a subject close to my heart — the purpose of this journal. It had been quite
some time since I had reminded our readers of our original purpose when we set
out some 20 years ago.
More than anything else, this journal has always been a “labor of love” for me.
It is the reason I founded the antenneX magazine almost 20 years ago, knowing
that running a magazine is a tough business and especially so since I planned to
do it without the traditional revenue support from advertisers or outside
investors. I wanted this magazine to always be able to write about any issue
without concerns of losing the support from any of those type revenues. I am
pleased to say, we have never steered from that course one iota. And, as a
consequence, we have covered some very controversial developments throughout the
past two decades. In the process, we have provided valuable factual information
to more than 200 countries, even to the most remote regions of the globe. Hence,
our readers are much more informed about the truth about all of the “new”
devices as their stories unfolded in the antenna and antenna-related field. For
more details, you are encouraged to read my column from September 2006.
Additionally, we were pleased to receive and publish in the October 2006 issue, a very special editorial reaction to my column written by one of our long-term readers and contributors, Dr. Jef Verborgt. Those two articles are located by the following links below:
VISIT THE GUEST ROOMS
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Along with the continuing fight against spam/virii junk, protecting our material and valuable bandwidth against piracy takes up a great amount of our time—time we can't really spare. The Internet is simply not the friendly neighborhood it used to be in the "old days" and more and more security must be installed to counteract these intruders. Thus, we have made the access to the Guest Rooms as automatic as possible for you to manage your own login.
http://www.antennex.com/guests.html
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In view of the above, we have overhauled the numerous free and open-access sections that have always been wide open to all of our friends throughout the many years antenneX has been online. But, we must change with the times as the need dictates. I don't think the Internet will become more friendly in the near future and protected sites with logins are fast becoming the rule rather than the exception. To repeat, most would like to know who they invite into their house. The same applies at the House of antenneX. It's really worth the effort!
This list pertains to those sections with free access now in our new Guest Rooms we have built and fully operating:
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The new Antenna Discussion List is a infinite fountain of ideas making it a great "watering hole" for exchange of ideas, questions and answers on a wide range of antenna-related subjects. You will be in good company along with some of the brightest minds available. Were else would you have such free access to this level of expert advice? To participate or just read along on some very interesting subjects each month with 2000+ members from all around the globe, you are welcome to join us:
You are encouraged to contribute your thoughts on various subjects to a worldwide audience.
AN INVITATION TO CONTRIBUTORS
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
manuscripts at antennex.com
. Do not feel that you must be ready to be a regular submitter to write for
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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.
To see details of our writing guidelines, please look at: Writing for antenneX
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IN THIS ISSUE
We again include many fine articles by our great writing team from around the globe. Now, allow me to introduce this month's line-up of content:
OUR MONTHLY COLUMNS (plus this one you are reading by yours truly):
FEATURE ARTICLES IN THE LIBRARY:
Sneaking Up on 2-Element Common-Feed Quads |
| Among 2-element quad beam users a question lingers. Which feed system is superior: separate switched drivers or drivers brought to a common feedpoint? The common-feed system is easier for the user, since it eliminates an extra, usually remote, switch box. However, the separate-feed system is usually easier to design and test for proper operation. Many answers to the question abound, ranging from antenna maker claims that users cannot always confirm to simple feelings about the matter. |
A Re-Examination of the Gamma Match Part 2 |
| There
are very few antenna designs that produce a perfect match to any given feedline, coaxial
or otherwise. Those that do are designed so as to compromise some other desirable antenna
characteristic. Many of the common commercial designs may use any of the following
matching systems e.g. The Beta and its close relative the Hairpin, Gamma or quarter wave
sections to achieve the desired match. A matching system is a necessity to minimize losses
along the feedline to the output transducer –the antenna. My aim is to review for the
readers the ‘Gamma Match’ so as to understand how it operates and hopefully
improve its performance. In Part I, the operation of the gamma match system was modeled as a series of transmission line equations. The mathematics above is very easily accomplished using a spreadsheet. I used Excel, part of my ‘Office 2000 package. The starting point will be the input impedance of the antenna. This must be the value of Zin, in series form, at the antenna terminals. As an example the results for a ‘Backyard Dipole’ are taken from the EZNEC (1) software as shown in this article. Now consider that we wish to use a Gamma Match with this antenna? It gets even more interesting. |
80–10
Meter Antenna System Impedance Matching: Part 4 |
| I continue
to struggle with the more popular use of 4:1 Ruthroff voltage baluns because invariably,
manufacturers of tuners include them for those using ladder or balanced line antenna
configurations. I suspect the continued availability of manufactured tuners are of the
unbalanced type is because of cost and popularity. Balanced tuners are obviously more
expensive since twice the number of components must be used and, in the case of variable
capacitors and inductors, they must be mechanically linked to allow simultaneous
adjustment. With a balanced network, the input needs can be satisfied by a 1:1 Guanella
type current balun that always sees its optimum surge impedance termination value allowing
maximum efficiency. There are many who use a balun at the antenna apex and accept the usual coaxial cable SWR loss. And the use of ladder or balanced transmission line is often impractical. Using a remote tuner placed at the antenna apex is equally impractical but in most cases, when considering one antenna for all amateur radio FCC approved bands, it would be the most efficient configuration and more acceptable regarding the use of coaxial cable rather than balanced transmission line. I shall discuss some of my findings and compare losses between balanced and unbalanced configurations. As in my previous articles, I shall show that the loss can be considered inconsequential for all practical purposes. But the losses invariably have to be accepted for the antenna system components and consequently can become an additional heating problem. This article will be a continuing exercise since a complete coverage of all variations would entail many pages of discussion. My first exercise will cover the popular use of the Ruthroff voltage balun that is not one of my favorite choices but is used by almost all antenna tuner manufacturers. |
Radiation in the Near Zone of a Short Center-Fed
Biconical Antenna |
The electromagnetic fields far from any antenna can be conveniently described as the sum of the radiation fields of oscillating point multipoles, of which the leading term is a dipole in many cases of practical interest. The form of the fields associated with the nth multipole is independent of the details of the physical layout of the antenna (other than that the layout determines the magnitudes of the multipole moments). However, close to the antenna the electromagnetic fields include quasistatic components as well as radiation terms. A well-known argument due to Hertz gives the fields in the near and far zone of an ideal point dipole. Here, we explore examples in which analytic expression can be given for the near and far zone fields of antennas of finite dimensions. |
Boris and Natasha’s Antenna |
I remember an episode of TV’s Rocky and Bullwinkle Show where Boris and Natasha were operating their spy radio, which had a diamond shaped old-fashioned antenna mounted on top of the console. I recently became curious about the performance of such an antenna, and I am guessing that it was a rotating spiral winding in the x-z plane. I saw one a long time ago that was wound with cotton-covered wire, but I am not sure about the routing of the wire. I am going to assume that the spiral started at the bottom and ended at the center, where the exit lead dropped back to the bottom, as shown in an illustration. I am also assuming that the height was 20 inches, and the number of turns was 10, producing a turn spacing of one inch. Thus the wire length is the sum of the four sides of each turn, which is about 8.5 feet — and so, off we go with this experiment as inspired by a cartoon show, but a classic one! |
Coaxial Cable Delay Measurements - Part I |
| "Besides the well known square-root-law loss increase with
frequency, there is also decrease in inductance per unit length effect in the models
described. Although most practical RF applications are well above the frequency where the
current flows through the whole cross-section of the inner wire, I would appreciate any
comment on the subject. With best regards, Vadim Demidov" During the month of October 2006, there was a rather lengthy discussion on the antenna-discussion List, kicked off by Vadim Demidov of Russia about the modeling of the "skin effect" (see above) This topic was discussed from many angles by numerous members of the list, including the author of this presentation that analyzes such effects on coaxial cables. Jacques Audet, a frequent contributor of antenneX,
goes on to say: |
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.-30-
Best reGARDS, Jack L. Stone, Publisher
jack@antennex.com
November 2006 antenneX Online Issue
#115
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December 31, 2010
