Old Geek Invents New Stick 262
the morgawr writes "According to the EE Times and Science Blog, a scientist at University of Rhode Island has developed a new type of antenna design that, by increasing the efficiency, performs as well as the convential quarter-wave design but is only 1/3 as large."
No details of operation (Score:5, Informative)
The other thing I saw was that you tuned the antenna for a frequency with components - does this mean potentiometers or does it mean scrapping it and buying another 2d helix tuned to the specific wavelenghth?
Bandwidth of the antenna (Score:5, Informative)
There are several parameters for an antenna system (receive parameters in parens):
Most compact designs trade bandwidth for performance - the work well at f=NNN.N MHz, but not well at f=NNN.N +
This gets to be REALLY important for wide band systems like CDMA and UWB.
Fractal antennas (Score:4, Informative)
Re:I doubt this will shorten AM towers (Score:5, Informative)
On the AM radio band the tower IS the antenna. What you see sticking up in the air is usually insulated from ground right at the base, the part you see is actually hot. Therefore the tower itself radiates and is engineered to be a certain height as part of antenna design.
Re:I doubt this will shorten AM towers (Score:5, Informative)
Long (LF) and medium wave (MF) antennas usually are the entire tower because of the low wavelength. For VHF (e.g. FM radio) and TV the antenna is much shorter so it is at the top of the tower.
One way to tell if it is not obvious is to look at the steel support ropes. If they are broken along their length with insulators then it is probably a long wave or medium wave antenna. The steel rope is broken in this way to prevent the wire being long enough to become a significant and undesireable part of the antenna.
Ham response (Score:5, Informative)
Re:Very promising! (Score:3, Informative)
Article also says that that antenna was of a limited-power design (maybe he used cheap and small 28-gauge wire, or something?) In any case, it says he refined his design after that.
-T
Re:I doubt this will shorten AM towers (Score:5, Informative)
As it says in the article, wet (and salty which I didn't know) ground is best for transmission. AM towers are often set in a group of three and set in low lying wetlands (near water especially). If you look closely, you will see that the only thing perched on top would be the strobes (if applicable).
Re:Ahh yes, but.... (Score:3, Informative)
Its the U.S. military's latest Active Denial System developed by Raytheon scheduled to start trials this fall. Its a millimeter wave beam weapon designed for non lethal crowd "control". Volunteers at Raytheon subjected to it described it as "unbearably painful, saying they felt as though their bodies were on fire". It should put an end to any unauthorized demonstrations against the U.S. or any of its allies. Its not entirely clear what happens to your eyes if you take the beam in the face at close range, or if it will cause cancer long term.
In case you think this is just Bush administration big brotherism, John Kerry is a big fan [counterpunch.org] too.
Re:Genetic Algorithm (Score:5, Informative)
The purpose for the Markland antanna is "stealth" - it can turn on and off and re-tune itself on the fly. It is also a directional antenna. The antenna in this story is a smaller form factor for a wide frequency range omni-directional antenna.
Basically they are apples and oranges.
Re:I doubt this will shorten AM towers (Score:3, Informative)
Um, all AM transmitter stations use the whole tower as the antenna. Actually, they also use the ground as the antenna, too - half the radiator is above ground, and the ground plane acts as the other half of the radiator. And since you need a good ground plane, a 200' antenna on top of a 200' tower would be awful - and if you used the lower 200' as your ground plane, you'd get no radiation whatsoever (you'd get a positive wave from the top 200' at the same time as you'd get a negative wave from the lower 200' and they would cancel once you were more than a short distance away).
IAARadioEngineer
-T
Re:Very promising! (Score:5, Informative)
Re:I doubt this will shorten AM towers (Score:5, Informative)
Just to add... since the entire tower is the radiator at AM frequencies, the multiple towers are used for directionality... just like in VHF and UHF (and cell) frequencies, multiple antennae are usually mounted on the towers (though it's tough to see individual antennas since they're usually placed either 1/4-wave or 1/2-wavelength apart... in VHF that would be about 6-10 feet).
So anyways, several AM towers in a straight line (like WEEI, 4 towers south of Boston, or many others - there's a 6-tower set just west of NYC) yield a sort of figure-8 pattern, with the lobes pointed in the same direction as the line of towers... usually an easy way to tell the direction to the nearest big city. There are also directional patterns that aren't so easy, like one of my sites, WRNI in Rhode Island, which has 4 towers, set in a sort of Y shape. 3 are used during the day for one pattern, and one of them turns off and a different one turns on a night for a different pattern.
-T
Re:Bandwidth of the antenna (Score:1, Informative)
An antenna structure has to overlap with the radiating dipole field, wich goes linear to zero at its center. So bigger antennas are better.
Higher multipole fields are even worse so why should there be other, better small antenna designs?
1
A small antenna has a to high impedance (>300 ohm = free space = trafo'ed coax)
If I put a high impedance cable in between two 50ohm cables, I get standing waves. Transmission at destinct frequencies it one.
high,long impedance jump = low VSWR bandwith?
Arne Rosenfeldt (his first slashdot post)
Show me the plots (Score:3, Informative)
Re:not possible (Score:4, Informative)
I am a physicist myself, currently doing materials research for the Navy. From time to time throughout my career, I have been approached by "inventors" with various ideas. I always give these schemes due consideration because, as another poster mentioned, one should keep an "open mind". But mainly because, even if the idea as a whole is nonsense, there may be elements of it that worth something.
There is a pattern. Almost all of the "inventions" that have been presented to me for evaluation and endorsement have made remarkable claims about "efficiency" approaching 100% -or in some cases exceeding 100%. This always turns out to be due to the inventor not recognizing and accounting for all the losses in the system, or making bad assumptions about efficiency being equal to some other factor (there are a few hams, for example, who mistakenly equate SWR with efficiency). There is another pattern to this sort of thing - that is, when I point out the error, they almost always accuse me of not having an "open mind" and I sometimes get a lecture from them about "paradigm shifts" or Einstein or Tesla and so on. etc. Then sometimes they proceed to harass me for months with minor variations of their idea. I always wonder why, if I don't have an "open mind" and am part of the entrenched establishment, why do they work so hard to try to get my endorsement!
Some of these have been pretty interesting ideas that have taken up to a week to study. Some of have been utter nonsense. I was even approached once by someone who claimed to have found some "particles" left behind by aliens who had abducted him, and he wanted me to "analyze" them. Well, I did an analysis and identified it to be a chuncks of Hartz hamster food. But that's another story.
I can't say whether the antenna inventor in this case might have approached someone in the physics department about this antenna, and if he did whether he was turned away, and if so, why.
Just suggesting that (1) we should not condemn the idea outright until we get some first-hand information on what the guy actually claimed - press releases don't necessary mean anything, and (2) if it's nonsense, it is not necessarily reflective of the University's research quality.
Re:I doubt this will shorten AM towers (Score:4, Informative)
An even easier way to tell is look where it's installed and how many towers there are.
"AM" radio (actually, MF broadcast) transmitter sites are almost exclusively found in low, wet, marshy land in order to maximize their groundwave coverage and to get a good counterpoise (RF ground).
Not just that, but many "AM" transmitter sites -- though certainly not all, however -- encompass a number of similar towers in an array, not just one or two. This is done in order to direct their signals in certain directions and to null out their signals in other directions (since MW broadcast signals carry over somewhat great distances after dark).
VHF Broadcast ("FM") and television trnasmitters, on the other hand, are located on high towers on the highest ground available. VHF and UHF are line of sight, hence the higher the better.
As previous posters have stated, "AM" transmitting antennae are the towers themselves. Using the equation 468/f (MHz), a quarter wavelength for 1000 kHz is 468 feet high! VHF antennae, on the other hand, are MUCH shorter and are mounted atop supporting towers.
Prior Art? (Score:2, Informative)
Patent Pending? (Score:2, Informative)
Re:Very promising! (Score:3, Informative)
Adjacet base towers use different frequencies to resolve exactly this kind of problem. The cell phone should be able to pick which one is best.
Re:I doubt this will shorten AM towers (Score:3, Informative)
Also, as much as possible is usually done to reduce the skywave portion of the radiation and confine it to the ground wave that goes out toward the horizon as oppose to shooting off into the sky, to either go forever in the daytime, or to be reflected back many hundreds of miles away by the changes in the night sky ionization layers, and wrecking havoc with another local station also sharing that frequency. To this end, they are often made 5/8 of a wavelength high since this is the maximum groundwave/least skywave pattern.
But, for small local stations, that gets quite expensive rapidly. My local am'er on 940 khz, would need a tower 654 feet high, well beyond his budget, so a much shorter tower is loaded to make it look longer electrically. Often, its only the so-called clear channel (read higher income) stations that can do that.
Cheers, Gene
Re:Very promising! (Score:3, Informative)
I was just pointing out that the original submitter and the comment I was replying to assumed he was a scientist at URI, when he was not. I also thought the NYT article was interesting enough to be submitted as an additional link.
Re:Patent Pending? (Score:3, Informative)
Very interesting (Score:1, Informative)
My only concern would be how "directed" this beam is. As crowd control it would probably be necessary to be able to cover a wide arc without disturbing innocent people in nearby businesses.
A Very Skeptical View (Score:5, Informative)
First, most PCS phone antennas don't have to be shortened. The wavelength is such that it's not hard to get 1/4 wave across your typical portable phone. It's a mere 4.1 cm.
Just so that most of you understand, a monopole antenna is really half of a folded dipole. It has a wire going up and then it goes back down the pole to a field of radials. It has a characteristic impedance of half what a folded dipole would be --about 150 ohms.
In contrast, a normal quarter wave vertical has a characteristic impedance of about 37 ohms (assuming a very good radial system).
Now, remember the part about heating up the antenna? The reason it happens with very short vertical antennas is because there is a current node right there at the base feedpoint. Even a small amount of resistance will generate heat. As you shorten the antenna the characteristic impedance drops. For anything less than a tenth of a wave long, it can drop to less than an ohm. At that point, ANY antenna resistance, even the normal resistance of copper or silver, becomes very relevant. If someone were to use a superconductor, it might make a very big difference.
So a shortened vertical isn't such a good deal. We use them because sometimes that's all we can afford to install on a mobile system. This is why most hams who operate on longer wavelength bands try to locate the loading coil closer to the middle of the antenna. It gets the loading coil away from the worst of the current node, reducing i^2r losses, and increasing efficiency.
Now, take the monopole: The current node is near the top of a quarter wave monopole, not the bottom. We still need a loading coil, however, so that we can match the impedance to something we'd expect a transmission line to have. If we shorten the monopole, we move the current node. The key is to move the current node away from the loading coil, because loading coils don't radiate well.
Thus, what this designer has done is to distribute the loading coil of a shortened monopole so that he avoids the current node.
There are problems, however. First, you still need an effective radial system. Without one, you simply won't have anything that radiates worth a damn. Second, while coil Q factor is less relevant where it stays away from the current node, it still has to be damned good. Further, the current node at the top needs to have very good surface conductivity.
Finally, no matter what, a shortened vertical antenna will have a shortened bandwidth, proportional to how much the antenna itself is shorter than a regular 1/4 wave. TNSTAAFL.
Don't misunderstand, a short antenna doesn't have to be inefficient. However efficiency is not the same thing as gain. Short antennas can not have much gain. That's a matter of physics and mathematics. And the shorter an efficient antenna gets, the less bandwidth it can cover. Despite the steady parade of publicists, that's the reality. Don't buy any snake oil, folks... This isn't really that novel.
This is probably just hype.... (Score:4, Informative)
The "gain" of an antenna comes purely from directional effects, in a transmitter, which is easier to understand, more of the radiation goes out near the horizontal, where it is useful, the apparent gain in receive mode is identical due to the reciprocity theorem. In any situation involving electromagnetic radiation, such as light, or even pressure waves such as sound, the directional properties are always limited by the dimension of the antenna, loudspeaker, lens, etc, in the case of a verticle monopole you really need height to get lots of low-angle radiation, for the same reason that radio telescopes of high angular resolution have several dishes spread out over a great distance, sometimes hundreds of miles. It is also why a 15 inch PA loudspeaker will give, on axis, maybe 102dB at 1 metre with 1 watt input, while an 8 inch hi-fi speaker may give only about 80dB. even though both are equally well made and have had similar attention to loss mechanisms. Likewise the best searchlights have large-diameter lenses....A human eye is large in comparison to the wavelenght of light, so it can resolve lots of detail, the eye of an insect can distinguish only vague impressions of light or colour. There are lots more examples.
Some years ago, the Crossed Field Antenna, which purported to be even smaller, made similar claims, backed up by real-life tests.... I am sure that Google will find lots of references, so why does every AM broadcast station not use one? Maybe 10 to 20 feet high, not too heavy, no expensive materials, yet do you ever see them? Again, it was correctly resonated, but it did not have the height.
In any case I am sure there will be a very large amount of prior art on this one, a fair proportion of CB antennae for instance use loading coils and helixes in just about every combination imaginable. The current distribution of monopole antennae has been widely studied for many years. I would like to see a picture of the thing, to see what, if anything, is new.
Also, the microwave end of the spectrum has no need of smaller antennae, no mobile phone I have seen in recent years has had an external antenna at all, and you can only make a phone so small.. You have to hold the thing, after all. If it is not entirely self-supporting in air, dielectric losses will be serious.
Re:Very promising! (Score:2, Informative)
And actually, it would improve BOTH battery life and reception, since receiving a signal doesn't require any more or less power based on the antenna or incoming signal strength (excepting preamps). All other things being equal, if you decrease the transmit power, increase the antenna gain (which gives a gain for both receive and transmit), then you use less power overall, but can output an equivalent signal.
Actually, your reasoning is a little flawed here. Yes, you would get improved tower to phone reception even if you reduced power proportional to antenna gain improvement but that degree of transmitter power reduction would cancel out the improvement in phone to tower reception. Since the radio signals have to travel in both directions to make a phone call, you still have to trade off reception vs power. However, the cell phone will probably do that for you automatically, since cell towers command phones to reduce power (so they don't interfere with other phones by causing receiver distortion) if the tower gets a signal more powerful than it needs. You will get your improved reception and improved battery life but not necessarily at the same time:
5X reception, 1X battery life,
1X reception, 5X battery life,
2X reception, 2.5X battery life,
etc.