Where Does Radiation Come From?
By Jack L. Stone, Publisher
respect for authority is the greatest enemy of truth.
-Albert Einstein, physicist, Nobel laureate (1879-1955)
his month is packed with antenna concepts, modeling, discussions, experiments and theoryall in a single issue! For instance, once again, Claudio Re, I1RFQ puts more of those "new antenna" claims to the test in his article this month "The DLM (Distributed Load Monopole) Antenna". I had asked Claudio to put this one on the top of his list for tests as so many readers had expressed an interest in the "new" device from Robert Vincent and the University of Rhode Island. Once again, Claudio's work is very straightforward and well explained. More about this below.
Next, our new contributor in this month's issue, Scott M. Harwood, K4VWK, and his article entitled "Using Extremely Short Antennas - Is the MicroVert an Answer?" revisits the popular MicroVert based on reading Juergen's construction article and the theory previously explained in an article by Werner Hödlmayr, DL6NDJ. Scott includes a description of his measurements on this new experiment and how well he thinks this design performs as a short radiator.
That is followed by more experiments by our monthly science writer Joel C. Hungerford in his article "More Experiments with the CCD Antenna." Last month, Joel explained how to build a CCD antenna. Here's one in the picture to the right in Joel's workshop. Looks like he has altered the design some more with an "eggbeater" top load!
CCD means "Controlled Current Distribution" and refers to distribution of RF current on a resonant antenna. The CCD first appeared here in 1989 in an article of antenneX by Jim Gray, W1XU. As Jim explained this antenna is of interest largely because:
It is ground immune:
Advantages of a CCD antenna compared with an ordinary wire antenna are many and important. For an example there is NO standing wave voltage on the antenna which means that the "end effects" are negligible. The CCD is relatively immune to ground and other objects because of this feature, and may be laid out on the ground and still operate effectively! This means also the CCD can be placed close to walls, tree branches, other antennas and objects, with very little interaction.
Has height and signal advantages:
The CCD appears to put out a better signal than an ordinary antenna at the same height, and seems to have a lower angle of radiation for a given height above ground. Keeping these advantages in mind, you should know that there are some disadvantages of a CCDmostly mechanical. It is a bit tedious to construct, it is twice as long as a conventional wire antenna, and it is a bit more expensive, too, because of the capacitors that must be placed every few feet from feedpoint to end.
Then, one more new contributor weighs in this month on a controversial subject, "displacement current" introduced earlier by Bill Miller in his series of articles. Fred E. Ellis, PhD, has presented his own opinions in his article Stop Blaming Displacement Current on Maxwell. This is with a very good explanation of the mathematical basis of the displacement currents presumed to exist in capacitorsbut Fred claims, we dont need to confront Maxwell in order to do this. Yes, with his ideas for experiments, Fred says lets pretend we never heard of Maxwells equations!
ROBERT VINCENT'S DLM ANTENNA TESTED
Recently some claims about new short but efficient antennas has been proposed from Robert Vincent and the University of Rhode Island in Kingston. Basically, this is what Robert Vincent tells about this new invention as published in some interviews:
"The DLM, or distributed load monopole antenna, is based on a lot of things that currently exist," said the researcher who invented the smaller antenna, Robert Vincent of the university's physics department, "but I've been able to put a combination of them together to create a revolutionary way of building antennas. It uses basically a helix plus a load coil. Using a DLM antenna one-third to one-ninth the size of standard quarter-wave antenna, I measured nearly 80 percent efficiency, when conventional wisdom would dictate that an antenna the size of a DLM should be only 8 to 15 percent efficient."
THE MICROVERT REVISITED
In April 2001, we published a couple of articles about an interesting antenna design called the MicroVert. One article, "The MicroVert" by Werner Hödlmayr DL6NDJ went into depth about the theory behind this unique atypical design while another, "The Marvelous DL7PE-MicroVert" by By Juergen Schaefer, DL7PE dealt mostly on the construction of his own design shown here in Photo 1.
The theory behind the MicroVert design apparently
emerged from a comprehensive literature reference (lucky those who read
German!) but the essential information is contained in a paper written by Prof. F. Landstorfer and Prof. H.
Meinke back in 1973 and published in the Nachrichtentechnische Zeitschrift Nr 26 with the
title A new equivalent circuit for the impedance of short radiators.
In this month's issue, we revisit the MicroVert through a fresh article about the experiments and construction of yet another MicroVert by another new contributor, Scott M. Harwood, K4VWK. Scott's new article is entitled "Using Extremely Short Antennas - Is the MicroVert an Answer?" based on reading Juergen's construction article. Scott also includes a description of his measurements and how well he thinks this design performs as a short radiator.
Scott Harwood, K4VWK
Scott Harwood, K4VWK, has been interested in radio since childhood. In the seventh grade he built a two-tube regenerative receiver using #30 tubes as a science project. He obtained his first amateur license in 1958 and has had the same call for over 40 years, and now is an Amateur Extra class.
After college and a tour in the USAF, Scott returned to Virginia, where he now resides. He has experimented with and developed antennas for the past 30 years. He and his wife, Susan, travel extensively, and his main area of interest has been small portable antennas for 160 and 80 meters. He has given talks at local radio clubs on antennas, and has written previously for CQ Magazine.
As I've stated before, the MicroVert remains a very
popular article in our Preview section among new visitors to our site. If you haven't seen
that one yet, it can be found freely available to read at:
bout eight (8) months ago in the antenna-discussion list, we had an extensive discussion about how radiation behaves on an antenna and especially about what makes the signal decide to jump off the device and head off in the right direction.
I had kicked off that earlier subject thread by asking:
"Most who deal with EM+antennas are probably familiar with the following definition of a photon:
"....The quantum of electromagnetic energy, generally regarded as a discrete particle having zero mass, no electric charge, and an indefinitely long lifetime...."
So, I ask an age-old question: "How does the photon without mass or electric charge, leap from the antenna...??? What makes it want to? " I seem to recall this has yet to be explained....
Many of our members joined in on this and we had a very interesting
and diversifieddiscussion about this most basic, but difficult to
Indeed the above discussion is not the first time that subject has been debated, nor will it be the last time. Sure enough, within the past week we have had another interesting discussion about this issue. That discussion is still in progress as I write this column (September 30, 2004). Here is just a portion of the discussion about this very basic apsect:
WHERE DOES RADIATION COME FROM ON AN ANTENNA?
Subject: [Antenna Discussion] Where does radiation come from on an antenna?
From: "Claes Johansen"
Date: Fri, 24 Sep 2004 19:20:06 +0200
is interesting that the textbooks do not explain where on an antenna radiation come from.
I think the reason is that it is not possible to experimentally verify or detect radiation
inside the near field zone. So nobody knows for sure.
|From: "Kirk T McDonald"
Date: Fri, 24 Sep 2004 18:16:52 -0400
Organization: Princeton University
To be frank, your email contains many misconceptions about radiation, which illustrate why continued effort is needed for antenna enthusiasts to come to a good understanding of how antennas radiate -- from the perspective that radiation consists of electromagnetic fields.
My major objection to your note is the notion that no radiation exists close to an antenna (i.e., in the near zone). If this were so antennas would have to operate by some kind of action at a distance, whereby the currents in the antenna cause effects far from the antenna without these effects propagating from the antenna to the remote site.
This is completely at odds with the idea of electromagnetic fields, which concepts were created precisely to avoid action at a distance.
A consistent understanding of the electromagnetic fields of an antenna MUST include a description of how the power that can be detected in the far zone has passed by all of the intervening points between the detector and the ultimate source of the rf power.
The usual lore, to which I subscribe, is that the key to an understanding of the flow of energy in electromagnetic fields is the Poynting vector.
Lines of the Poynting vector CANNOT begin (or end) at some point in empty space. They can only begin at a place where energy is being transformed into electromagnetic field energy from some other type of energy.
Thus, thinking about antennas from the perspective of energy, and energy flow, the more basic notion of conservation of energy (which can be transformed or moved around, but neither created nor destroyed), we will come to accept the view that an antenna directs the radiation from the rf generator, but does not itself create the radiation.
Then, is it not surprising that a proper calculation of the Poynting vector close to an antenna shows that no lines of the Poynting vector actually touch the antenna -- although they can be parallel to the surface of the conductors of the antenna.
Rather, the lines of the Poynting vector emerge from the rf generator, pass down the (coaxial) feedline, and emerge at the antenna feedpoint where they "radiate" outwards and quickly arrange themselves into the far-field radiation pattern.
It is impressive how beautifully the NEC calculations of the Poynting vector agree with the basic notions of conservation of energy. The program is working well!
Ignoring the lessons of conservation of energy, and their successful illustration by the NEC computer programs is not a good path to understanding of antennas!
...................... However, I acknowledge that many people can have objections to the above view, based on the feeling that their antennas are more the just wave guides. After all, they do contain oscillating currents, which involve accelerating charges, and it is well known that accelerating charges radiate electromagnetic waves.
But one must maintain a healthy perspective. For example, a mirror involves the absorption of energy from the incident wave, which accelerates the electrons in the mirror, which then radiate in a manner that exactly cancels the incident wave on the back side of the mirror, and which produces the reflected wave on the front side of the mirror. Yet, most of us would not say that a mirror "creates" radiation. Rather, it is a passive device that responds to external stimulus by "reflection".
An antenna is more sophisticated than a passive mirror. But it is consistent to think of an antenna as a kind of "active mirror", which performs a subtler task than simple reflection. The pattern of currents in an antenna shapes the input waves from the rf
generator into far field patterns that could not be obtained by simple reflection.
................ It may be instructive to consider the Poynting vector of a mirror.
We could say that the incident wave has a Poynting vector the points towards the mirror, and the reflected wave has a Poynting vector that points away from the mirror.
But, what is the Poynting vector of the total field = incident + reflected?
For example, suppose that
E_in = E_x cos(kz - omega t), in the x direction
H_in = H_y cos(kz - omega t) ,in the y direction
S_in = E_in x H_in = E_x H_y cos^2(kz - omega t), in the +z direction
For an observer at a fixed z, the time-averaged Poynting vector is
S_in_ave = E_x H_y / 2, in the + z direction
If the mirror is at z = 0, the reflected wave is
E_r = -E_x cos(kz + omega t), in the x direction
H_r = H_y cos(kz + omega t), in the y direction
S_r = E_r x H_r = E_x H_y cos^2(kz + omega t), in the -z direction
For an observer at a fixed z, the time-averaged Poynting vector is
S_r_ave = E_x H_y / 2, in the - z direction
The total average power flowing past the observer is ZERO!
Let's see if we can confirm this by consideration of the total fields.
E_tot = E_in + E_r = E_x [cos(kz - omega t) - cos(kx + omega t)]
= 2E_x cos(kz) cos(omega t)
H_tot = H_in + H_r = H_y[cos(kz - omega t) + cos(kx + omega t)]
= 2H_y sin(kz) sin(omega t)
S_tot = E_tot x H_tot = 4 E_x H_y cos(kz) sin(kz) cos(omega t) sin(omega t).
The time average of this is indeed ZERO.
What is the lesson here that might be relevant for our thinking about antennas?
Namely, if you consider only the TOTAL Poynting vector of a mirror, you would think that a mirror is a dull device, since the total (time average) Poynting vector is zero.
So, perhaps the total Poynting vector of an antenna does not tell us everything about the flow of energy that we'd like to know.
Maybe we need to partition the fields of an antenna into two appropriate pieces, and consider the Poynting vectors of these two pieces separately.
But, how to do this partitioning?????
I propose the following:
1. Use the NEC program to calculate the total fields AND the currents in the antenna.
2. Ask the NEC program to calculate the fields due to the currents, taken as given input, rather than as something to be deduce. This might be a tricky step, since this is not the way NEC programs normally work. The NEC program can then, of course, calculate the Poynting vector of the fields produced by the currents.
I believe that this Poynting vector will make many people happy. It will be what they regard as the proper Poynting vector of the antenna. The lines of this Poynting vector will emerge from points on the surface of the antenna, not from the feed point.
3. Take the difference between the total fields from part 1 and the fields calculated in part 2.
Calculate the Poynting vector of the difference fields.
What will this look like?
I believe that this Poynting vector will emerge from the feedpoint of the antenna, and quickly curl around and end on the antenna itself.
That is, the 3rd Poynting vector will describe the flow of power from the feedpoint to points on the antenna. The 2nd Poynting vector will describe the flow of power from points on the antenna out into the far zone.
The first Poynting vector describes the flow of power from the feedpoint directly into the far zone, without appearing to get involved with the conductors of the antenna.
No textbook includes this kind of discussion. It is just not possible to do the calculations analytically, so textbooks don't even mention the calculation. Only with a computer program can we carry out steps 1-3.
I find all this rather salutary. Although antennas have been around for 115 years, textbooks do not give a decent discussion of real antennas that emphasizes flow of energy (i.e., radiation) in a complete and consistent manner. Because the calculations are difficult, the textbooks give only partial results -- without acknowledging that their presentations are incomplete. This allows reasonable people to come away with the impression that antennas are mysterious, perhaps magical objects that are not very well understood scientifically.
Personally, I would very much like to complete the numerical analysis proposed above, and use it to get on record the long-missing consistent story of the energy flow (Poynting vector) of real antennas.
|From: "Claes Johansen"
Date: Sat, 25 Sep 2004 04:57:11 +0200
Thank you for your kind and long answer. However it is easier for me to accept that the two fields expands separately to a distance where they match each other to space impedance, then it is to accept that there is any transverse electric field along the surface of the conductor. The electric field lines must leave the surface perpendicular.
I will have a deeper look into your answer.
|From: "Kirk T McDonald"
Date: Sat, 25 Sep 2004 13:43:32 -0400
Organization: Princeton University
Indeed, the electric field lines must, and do, leave the surface of the conductors of the antenna at right angles to the surface.
This is the core of the "antenna paradox".
Since the Poynting vector is always perpendicular to the electric field, we conclude that the Poynting vector must be parallel to the surface of the conductors of the antenna.
This is confirmed by the NEC calculations.
But it implies that the Poynting vector cannot NOT come from the conductors of the antenna!
So, if you also accept that the Poynting vector describes the flow of energy, i.e., the path of the radiation, we are led to conclude that the radiation does NOT come from the conductors of the antenna!
This is the antenna paradox.....
The NEC calculations illustrate Schelkunoff's resolution of the paradox: the radiation (and the lines of Poynting vector) comes from the feedpoint of the antenna. (And, the lines of Poynting vector can be traced backwards from the feedpoint to the rf generator, as those lines flow in the space between the inner and outer conductor of the coaxial feed cable.)
|.....continued as others join in on
the Antenna Discussion List.
For much more of this continuing discussion, as well as a wide spread of other subjects, you are invited go to the list web archives:
- Subscribed Members of the List
- To Subscribe to the list Archives and read only
- To Subscribe to the list to Post & participate
WHERE IS THE CURRENT?
Of late, nothing about Maxwells Equations have been so controversial perhaps as his part dealing with displacement current and whether or not it does or does not exist. One reason perhaps for the spirited debates is whether or not to take the term literal, as we know, understand and define it today.
For the past year or so, Bill Miller has authored several gutsy articles claiming Maxwells claim of displacement current in his equations doesnt exist and as one might expect, he has been called to task to prove such an almost sacrilegious claim!
Not to be deterred, Bill is forging ahead and working on ways to demonstrate proof of his hypothesis. Indeed, it will take more than just rhetoric to undermine those previous assumptions about Maxwells DC premise. Although Bill is still in a minority position until he has better proof, he has my support and encouragement to continue with his experiments because no matter how they turn out, we all learn from themand thats a good thing! Plus, Bill has the feeling of the vigor and excitement when one feels they are on the edge of discovery! This is what gives one the fuel to propel ahead against the odds and achieve something unique.
LET'S DO IT WITHOUT MAXWELL'S HELP!
In one of Bills articles in pursuit of the above, he made a presentation of how he believes a capacitor worksagain, a controversial debate stemmed from that as it relates to the so-called displacement current and Maxwell.
This month, a new author, Fred E. Ellis, with a physics PhD, has presented his own opinions in his article Stop Blaming Displacement Current on Maxwell. This is with a very good explanation of the mathematical basis of the displacement currents presumed to exist in capacitorsbut Fred claims, we dont need to confront Maxwell in order to do this. Yes, with his ideas for experiments, Fred says lets pretend we never heard of Maxwells equations!
new author Fred E. Ellis, AC5SO:
Fred has a PhD in physics with math minor from Louisiana State University. Earlier, he obtained two degrees (BS and MS) from East Texas State. While an undergraduate, he worked at radio station KGVL as a broadcast engineer.
Fred has been on physics faculties at East Texas State, University of Southern Mississippi, and Pan American College, which became University of Texas--Pan American.
After reaching retirement, he returned to his first love, radio, followed by antennas, which now get most of Fred's attention (and spare money!). His old ham license expired years ago, and after retiring, he hit the code hard to pass the 20 wpm exam, took all the written exams, and was back on the air as AC5SO.
Music is Fred's favorite pastime for relaxing and listens mostly to 17th, 18th and 19th-century compositions.
Freds article contains an especially important pointthe establishment of a certain laboratory experiment with a capacitor to potentially measure or otherwise determine the factors making up the two terms of the delta equation. This raises the question of what precisely would such an experiment look like? How would one go about making decisive measurements and what insights does the author have to offer on what the experimenter may find?
The author is careful to show that the key expression is mathematically a current expression, since it answers to current units corresponding to those applicable to the conduction current. He is also careful not to say what the expression means physically. Hence, the capacitor experiment that he notes has significance that is worth exploring deeper.
This leads me to suggest that Bill, Fred and Werner (and any others, perhaps?) should perhaps join forces on this issue of displacement currenteven though their views may (or may not) differ. Also, I have suggested to Bill that he would probably need to employ the use of calculus in this projectsomething that Fred manages to utilize in his mathematical presentation this month. I have a feeling that if Bill and Fred were to put their heads together with open minds, some interesting results would emerge. Bill is struggling to communicate his ideas and perhaps Fred could translate with his use of calculus language so that all the rest of us could follow and see the strengthsor flaws. Putting heads together on projects is one of antenneXs main endeavorsthen let the readers decide the outcome.
I will more than happy to assist in making the introductions necessary to bring together those interested in this project so that either Bill convinces usor he sees the flaw(s) some others see. E-mail: Displacement Current Project
ONE MORE COUNTRY JOINED LAST MONTH!
Country number 191 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 DEMOCRATIC REPUBLIC OF
THE CONGO, COUNTRY #191
Straddling the equator, the DRC is located in Central Africa, northeast of Angola at coordinates 0 00 N, 25 00 E.
It has a population of more than 58 million. Estimates for this country explicitly take into account the effects of excess mortality due to AIDS; this can result in lower life expectancy, higher infant mortality and death rates, lower population and growth rates, and changes in the distribution of population by age and sex than would otherwise be expected. Life expectancy is 47 for the male and 51 for the female.
They have over 200 African ethnic groups of which the majority are Bantu; the four largest tribes - Mongo, Luba, Kongo (all Bantu), and the Mangbetu-Azande (Hamitic) make up about 45% of the population.
Languages consist of: French (official), Lingala (a lingua franca trade language), Kingwana (a dialect of Kiswahili or Swahili), Kikongo, Tshiluba.
Rich in natural resources, it possesses cobalt, copper, cadmium, petroleum, industrial and gem diamonds, gold, silver, zinc, manganese, tin, germanium, uranium, radium, bauxite, iron ore, coal, hydropower, and timber.
Since 1997, the Democratic Republic of the Congo (DROC; formerly called Zaire) has been rent by ethnic strife and civil war, touched off by a massive inflow in 1994 of refugees from the fighting in Rwanda and Burundi. The government of former president MOBUTU Sese Seko was toppled by a rebellion led by Laurent KABILA in May 1997; his regime was subsequently challenged by a Rwanda- and Uganda-backed rebellion in August 1998. Troops from Zimbabwe, Angola, Namibia, Chad, and Sudan intervened to support the Kinshasa regime. A cease-fire was signed on 10 July 1999 by the DROC, Zimbabwe, Angola, Uganda, Namibia, Rwanda, and Congolese armed rebel groups, but sporadic fighting continued. KABILA was assassinated on 16 January 2001 and his son Joseph KABILA was named head of state ten days later. In October 2002, the new president was successful in getting occupying Rwandan forces to withdraw from eastern Congo; two months later, an agreement was signed by all remaining warring parties to end the fighting and set up a government of national unity.
Telephones - main lines in use: 10,000 (2002)
Telephones - mobile cellular: 1 million (2003)
Telephone system: general assessment: poor
domestic: barely adequate wire and microwave radio relay service in and between urban areas; domestic satellite system with 14 earth stations
international: country code - 243; satellite earth station - 1 Intelsat (Atlantic Ocean)
Radio broadcast stations: AM 3, FM 11, short-wave 2 (2001)
Television broadcast stations: 4 (2001)
Internet country code: .cd
Internet hosts: 153 (2003)
Internet users: 50,000 (2002)
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.
If you havent already joined, you are invited and encouraged to do so. Just click here and follow the instructions on how to join and have fun with the rest of us. If you don't participateit's a big opportunity lost!
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 readershipfor 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 firstname.lastname@example.org . 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 forwe shall always make room for a worthy article.
To see details of our writing guidelines, please look at: Writing for antenneX
Subscribe for the Premium Feature Articles!
Enjoy these new concepts with our readership: Be sure your subscription is active so you don't miss these new and exciting concepts and more to follow. If you are thinking about subscribing or renewing, save 21% with the 2-year subscription. Just go to this URL and check on the Subscription option of your choice.
Keep the issues coming and stay on the leading edge of antenna technology!
~ BE SURE TO VISIT THE SHOPPING SHACK ~
Shipments worldwide ~ plus instant downloads
| Subscription | Books | Software | Antennas | Components |
IN THIS ISSUE
This month is our 90th online issue online! We again include many fine articles by our great writing team. Now, allow me now to introduce this month's line-up of content:
THE OCTOBER 2004 ONLINE ISSUE NO. 90 CONTENTS:
OUR MONTHLY COLUMNS (plus this one by yours truly):
Investigators have suspected that a number of very small antennas do not themselves have significant radiation. Instead, the so-called antenna structures form non-radiating or very low-level radiating structures, and the main radiation from the antenna assembly as a whole occurs from the outer surface of the braid of the coaxial cable feedline. Most of the tests so far performed lack one essential ingredient to an unambiguous test result: one or more standards against which to compare the system under study. These notes are designed to suggest a standard against which to compare subject antennas.
FEATURE ARTICLES IN THE LIBRARY:
Needs Call for Special Antennas:
the following scenarios:
1. A repeater station is located on the coastline of a given area. The desired coverage area is inland, with no maritime activity.
2. Another repeater station is located near or at the base of a hill or mountain. It suffers from reflected signals returning from the hill surface. The desired coverage area lies in front of the hill and to the sides of the repeater antenna site.
3. A proposed repeater antenna site (and frequency allocation) lies close enough to another repeater's coverage area on the same or a nearby frequency to promise overlapping coverage and mutual interference. The new station desires an area of coverage that lies in the region not covered by the existing repeater.
These samples of special needs have in common a very similar desired region of coverage, but very different reasons for wanting that coverage. We might nearly endlessly create other plausible scenarios to provide other avenues to the same need. In each case, we need at least a semi-circle of coverage, with extensions to the rear. However, we need to diminish the signal to the rear for at least 60 degrees either side of a hypothetical center line.
We can, of course, design a complex array of multiple antennas to create the semi-circle-plus. However, if we can develop a single antenna to do the job, we obtain a maintenance advantage in terms of the mechanical and electrical simplicity of the installation. Notice that forward gain is not one of the criteria for the antenna installation. Anything close to the gain of a vertical dipole at an equivalent height would suffice. The major specification for this antenna installation--whatever the reasons behind it--is the pattern shape.
Experiments with a CCD Antenna
"Controlled Current Distribution" and refers to distribution of RF current on a
resonant antenna. The CCD first appeared here in 1989 in an article of antenneX
by Jim Gray, W1XU. As Jim explained this antenna is of interest largely because:
Last month, Joel explained how to build a CCD antenna. Here's one in the picture to the right in Joel's workshop. Looks like he has altered the design some more with an "eggbeater" top load!
Final Yagi-Uda 2-Meter 12-Element Beam Design
|Fred says his final 2-meter 12-element Yagi-Uda array design will concentrate on increasing the secondary lobe attenuation with some sacrifice in gain. However, a compromise will address SWR and secondary lobe attenuation. Optimization of gain, SWR, impedance, or secondary lobe attenuation alone only sacrifices the others desired characteristics. In order to accomplish this compromise, Fred uses his conjugate-gradient optimization (CGO) approach. This differs from the manual Optimized Wide-band Antenna (OWA) process and allows him to carefully arrive at the best-compromise design (BCD). In conducting this exercise, it is recognized that great care must be exercised as otherwise, the BCD will not be experienced, and many good designs will be lost. Fred explains how!|
DLM (Distributed Load Monopole) Antenna
some claims about new short but efficient antennas has been proposed from Robert Vincent
and the University of Rhode Island in Kingston. Basically, this is what Robert Vincent
tells about this new invention as published in some interviews:
"The DLM, or distributed load monopole antenna, is based on a lot of things that currently exist," said the researcher who invented the smaller antenna, Robert Vincent of the university's physics department, "but I've been able to put a combination of them together to create a revolutionary way of building antennas. It uses basically a helix plus a load coil. Using a DLM antenna one-third to one-ninth the size of standard quarter-wave antenna, I measured nearly 80 percent efficiency, when conventional wisdom would dictate that an antenna the size of a DLM should be only 8 to 15 percent efficient.
Once again, Claudio Re, I1RFQ puts another of those "new antenna" claims to the test in his article this month "The DLM (Distributed Load Monopole) Antenna". Claudio was asked to put this one on the top of his list for tests as so many readers had expressed an interest in the "new" device. Well, here it is. Once again, Claudio's work is very straightforward and well explained.
Blaming Displacement Current on Maxwell
|Another new contributor weighs in this month on a controversial subject, "displacement current" introduced earlier by Bill Miller in his series of articles. Fred E. Ellis, PhD, has presented his own opinions in this article. This is with a very good explanation of the mathematical basis of the displacement currents presumed to exist in capacitorsbut Fred claims, we dont need to confront Maxwell in order to do this. Yes, with his ideas for experiments, Fred says lets pretend we never heard of Maxwells equations!|
Extremely Short Antennas
the MicroVert buffs, our new contributor in this month's issue, Scott M. Harwood, K4VWK,
and this article revisits the popular MicroVert based on reading Juergen's construction
article and the theory previously explained by Werner Hödlmayr, DL6NDJ. Scott includes a
description of his measurements on this new experiment and how well he thinks this design
performs as a short radiator.
The theory behind the MicroVert design apparently emerged from a comprehensive literature reference, but the essential information is contained in a paper written by Prof. F. Landstorfer and Prof. H. Meinke back in 1973 and published in the Nachrichtentechnische Zeitschrift Nr 26 with the title A new equivalent circuit for the impedance of short radiators.
Well, there you have it, folksthanks 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. October
2004 antenneX Online Issue #90
reGARDS, Jack L. Stone, Publisher email@example.com
Send mail to firstname.lastname@example.org
with questions or comments.
Copyright © 1988-2011 All rights reserved - antenneX©
Last modified: December 31, 2010