[opendtv] Re: Anetnna design breakthrough?
- From: "John A. Limpert" <jlimpert@xxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 19 Jun 2004 13:22:00 -0400
I'd like to know how the design avoids the restricted bandwidth (high Q)
that always seems to be a problem with loaded antennas.
on 6/18/04 15:14, Manfredi, Albert E at albert.e.manfredi@xxxxxxxxxx wrote:
> This could be really interesting. Here's my take. Traditional
> antennas have current and voltage peaks and nulls along the length
> of each element. If an antenna is designed for constant current
> throughout each element, then its efficiency can be greatly
> increased. So the element -- he used a monopole design -- is
> provided with distributed L and C tuned to the carrier frequency.
> The results are amazing. Could be a big improvement to indoor
> antenna design, for example.
>
> The article addresses transmitter antennas, but the same should
> work for receiving antennas. More effeciency for the same size,
> or smaller sizes than traditional indoor antennas for the same
> signal strength. The 21 MHz example went from a 12 to 24 foot
> monopole to a 1.5 foot monopole.
>
> These are vertical monopoles. I'd like to see how this
> translates to horizontal dipoles, and the effect it might
> have on antenna height. At very least, you should see VHF
> antennas that are about the size of UHF antennas.
>
> This seems to be an elaboration of the traditional load coil
> used, for example, to match an FM monopole to CB frequencies.
>
> Bert
>
> ------------------------------------
> Antenna design boosts efficiency per given size
> By R. Colin Johnson , EE Times
> June 09, 2004 (2:28 PM EDT)
> URL: http://www.eet.com/article/showArticle.jhtml?articleId=3D21600147
>
> Portland, Ore. - A four-year skunk works effort at the University
> of Rhode Island in Kingston has cut the size of an antenna by as
> much as one-third for any frequency from the kHz to the GHz range.
> Using conventional components, the four-part antenna design cancels
> out normal inductive loading, thereby linearizing the energy
> radiation along its mast and enabling the smaller size.=20
>
> "The DLM [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."
>
> The patent-pending design could transform every antenna-from the
> GHz models for cell phones to the giant, kHz AM antennas that stud
> the high ground of metropolitan areas-Vincent said.
>
> For cell phones, for example, Vincent said he has a completely
> planar design that is less than a third the size of today's cell
> phone antennas. And those 300-foot tall antennas for the 900-kHz
> AM band that dominate skylines would have to be only 80 feet high,
> with no compromise in performance, using Vincent's design, he said.
>
> "When looking at these antennas, you pretty much have to forget
> everything you ever knew about antennas and keep an open mind,
> because some of the things I have done are very radical," said
> Vincent. "With my technique, I reduce the inductive loading that is
> normally required to resonate the antenna by as much as 75 percent
> . . . by utilizing the distributed capacitance around the antenna."
>
> NIMBY factor
>
> Vincent, an amateur radio operator, embarked on his project after
> he moved to a new neighborhood and his neighbors objected to the
> 140-foot tall antenna he planned to erect for a quarter-wave 1.8-MHz
> transmitter. So he surveyed the literature, took the best of the
> best designs and combined them into a 21-MHz test antenna that was
> 18 inches high, as opposed to the 12- to 24-foot height of the
> antennas normally used for that band. Building on that work, he
> eventually devised a 46-foot-tall 1.8-MHz antenna his neighbors
> could accept.
>
> "I looked at all the different approaches used to make antennas
> smaller, and there seemed to be good and bad aspects" to each,
> Vincent said. "A helix antenna is normally known to be a core
> radiator, because the current profile drops off rapidly; they are
> just an inductor, and inductance does not like to see changes in
> current, so it's going to buck that. "But what I found was that for
> any smaller antenna, if you place a load coil in the middle you can
> normalize and make the current through the helix unity; that is,
> you can maximize it and linearize it."
>
> Vincent has verified designs from 1.8 MHz to 200 MHz by measuring
> and characterizing the behavior of his DLM antenna compared with a
> normal quarter-wave antenna of the same frequency. He found that
> many of the disadvantages of traditional antennas were not problems
> for the much lighter inductive loading in a DLM.
>
> "For instance, in a normal quarter-wave antenna the current
> continually drops off in a sinusoidal shape, but these antennas
> don't do that," said Vincent. "The current at the top of the
> antenna is 80 percent of the current at the base."
>
> The reason more current can be pumped into a DLM design than in a
> conventional equivalent at the same size, Vincent theorized, is that
> the DLM distributes energy more evenly along the antenna's length.
> Using a DLM antenna one-third to one-ninth the size of standard
> quarter-wave antenna, he 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.
>
> To check his theory, Vincent analyzed and compared the current
> profiles, output power and a score of other standard tests for
> measuring antenna performance. All measurements were in reference to
> comparative measurements made on a quarter-wave vertical antenna for
> the same frequency, on the same ground system and same power input.
>
> "I was able to increase the current profile of the antenna over a
> quarter-wave by as much as two to 2.5 times," said Vincent. "That is,
> the magnitude of the current in these antennas is two to 2.5 times
> larger than for a normal quarter-wave antenna.
>
> "However, if you measure the current profiles for both antennas and
> integrate the area under the curves, you come out with the same
> volume, indicating that the much smaller antenna is filling the
> airwaves with the same amount of radio energy."
>
> Vincent plans to publish the results in a scientific journal soon,
> but with a patent decision imminent, he couldn't hold off a
> preliminary announcement that his theories regarding DLM antennas
> were being supported by the experimental results. According to the
> researcher, the DLM antenna profiles look just like the
> theoretically ideal antenna profile-operating on a single frequency
> with very high efficiency, while not producing any interfering
> frequencies or wasting thermal energy.
>
> "The phase and amplitude of this antenna are a perfect mimic of the
> universal resonance curve," said Vincent. "This makes the antenna
> completely predictable well beyond its bandwidth. Another unique
> feature is that these antennas have no harmonic response whatsoever;
> as a matter of fact, to a certain extent I used filter synthesis to
> design the antennas."
>
> Nondescript
>
> To the naked eye, the DLM antenna looks unremarkable, said Vincent,
> who jokes that you could put a flag on his antennas and they would
> look like flagpoles. But under the skin are four main sections to
> the antenna (from bottom to top): an inductive helix, a capacitive
> midsection, an inductive load coil and a capacitive top section.
> The different lengths of the mid- and top sections give them
> different resonant frequencies, which, together with the exact
> values of inductance and capacitance, define the antennas design
> specifications for any desired frequency.
>
> "The technology is completely scalable: Take the component values
> and divide them by two, and you get twice the frequency; take all
> the component values and multiply them by two, and you are at half
> the frequency," said Vincent. "There are two poles in the antenna,
> and where I place the poles in relation to one another-how much I
> bring the two resonant frequencies together or spread them apart-
> enables me to emulate different antennas, from a quarter-wave to
> a five-eighths wave."
>
> Vincent said no existing modeling software could adequately model
> his antenna design. So he rolled his own simulation with Mathcad,
> making use of some of Mathcad's filter design algorithms for the
> inductive/capacitive-canceling effect.
>
> "Eight years ago, antenna design was 90 percent black magic and 10
> percent theory," said Vincent. "But now, with my design, they are
> 10 percent black magic and 90 percent theory."
>
> The antennas are also well-behaved, with wide bandwidth and easy
> to connect to standard equipment, according to Vincent. For
> instance, they can directly connect to standard 50-ohm antenna
> inputs without any adapters.
>
> "All I have to do is tap the helix at its base, and you get a
> perfect 50-ohm match with out any lossy networks [as are required
> for other advanced antenna designs]," said Vincent.
>
> For the future, Vincent is moving up into the GHz bands for use
> with cell phones and radio-frequency ID equipment. A problem in
> the past has been that as components are downsized, they become
> too small to utilize standard antenna materials. At 1 GHz, for
> example, the helix is only eight-thousandths of an inch in
> diameter and requires more than 100 turns of wire.
>
> "So I came up with a new way of developing a helix for high
> frequencies that is a fully planar design; it's a two-dimensional
> helix," said Vincent.
>
> With the new helix design, Vincent has built a prototype 7-GHz
> antenna that he claims is indistinguishable from a quarter-wave
> antenna in all but its size. "Because the new design is
> completely planar, we could crank these out using thin-film
> technologies," Vincent said.
>
> Vincent received the 2004 Outstanding Intellectual Property Award
> from the University of Rhode Island's Research Office, joint
> applicant for the patent.
>
> Copyright =A9 2003 CMP Media
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