[HCRA] Antenna Design

[Larry Krainson]

A friend sent me this article from the NY Times.

Enjoy,

de WB1DBY

>
> Intriguing the Physicists, Radio Buff Shrinks an Antenna
>
> June 10, 2004
>  By IAN AUSTEN
>
>
>
>
>
> WHILE a lifetime in ham radio played a role, it was love
> that ultimately led Rob Vincent to develop what he says is
> a way to make antennas significantly smaller but still efficient.
>
> "About 1995 I had met a sweetheart and we fell in love,"
> Mr. Vincent, now 60, recalled. "I went to live with her,
> but the only problem was that she lived on this postage
> stamp of a yard in a congested neighborhood."
>
> The real estate owned by Carolyn Hardie, the woman Mr.
> Vincent later married, was an issue because his amateur
> radio interests had turned toward frequencies in the
> 160-meter band. That band is close to broadcast AM radio.
> And, like an AM station, operating on it requires a tall antenna - in
> Mr. Vincent's case, one that is 140 feet high. Aesthetic and zoning
> questions aside, the 50-by-100 foot lot was not big enough to
> accommodate the guy wires needed to stabilize a tower that high.
>
> So Mr. Vincent, a technician with the University of Rhode Island's
> physics department, began thinking about ways to make antennas smaller.
> The end result is a system that he claims can produce antennas that are
> one-third to one-ninth as high as normally required. He has spoken to
> other ham operators in over 80 countries on the 160-meter band through
> his relatively new, self-supported backyard tower, which is one-third of
> the conventional minimum size.
>
> Mr. Vincent said his improvements were not just applicable
> to ham radio towers. They could be used to either further shrink the
> tiny antennas in cellphones, he said, or boost their efficiency.
>
> Small yet efficient antennas have long been a goal for
> radio researchers, said R. Dean Straw, the senior assistant technical
> editor for the American Radio Relay League, an association of amateur
> operators. "The holy grail is an antenna the size of a grain of salt
> that produces big signals," he said.
>
> Generally the size of antennas increases with the
> wavelength of the frequencies they are transmitting or receiving. While
> there are several formulas for determining optimum height, the height of
> most antennas is one-quarter to one-half the wavelength. At 140 feet,
> for instance, Mr. Vincent's ham tower would have been slightly higher
> than one-quarter of the wavelength of 160 meters, which is equal to 525
> feet.
>
> Smaller antennas can be used, but with a trade-off. "When
> you get below a quarter-wavelength, efficiency drops off dramatically,"
> Mr. Vincent said.
>
> Before arriving at the university in the early 1990's in a
> still-unfulfilled quest to complete his undergraduate degree, Mr.
> Vincent spent about 30 years in radio-related engineering jobs, mostly
> with a radar division of Raytheon. But his tinkering with antennas dates
> back to when he obtained his first amateur radio license at the age of
> 14.
>
> "I've always had a natural understanding of radio - maybe
> it's from a prior life," Mr. Vincent said. "But in those
> early days I could not fathom how an antenna worked."
>
> The relationship between antenna height and efficiency was
> so well established that he initially kept his antenna-shrinking work a
> secret. Mr. Vincent also acknowledged that he had relatively little idea
> of what might work when he began the project.
>
> "When I started out to do this it was 10 percent theory and
> 90 percent black magic," he said. After reviewing much of
> the literature, Mr. Vincent started designing antennas with special
> simulation software on a personal computer.
>
> From the most promising of those virtual designs, he ran
> tests using antennas that were about 18 inches high and fashioned from
> copper-covered Plexiglas rods. One model seemed particularly successful
> until it lost its signal during a high-powered broadcast test. When Mr.
> Vincent went outside, he found only a lump of molten metal and plastic.
>
> Gradually, he said, potential areas of improvement became apparent. He
> began confiding in some friends from the ham radio world and faculty
> members in the physics department. One friend allowed Mr. Vincent to
> build a 46-foot-high experimental antenna at his country home, which
> includes a salt marsh.
>
> Saltwater is an antenna builder's dream. By providing a
> highly conductive base for the antenna, the water improves reception.
>
> The big prototype improved upon conventional designs in
> many ways. But one crucial one involved the placement of devices known
> as load coils along its length. Load coils are commonly used in
> cellphone antennas to alter their current patterns.
>
> Conventional broadcast antennas, Mr. Vincent said,
> generally have a lot of current at the bottom and very
> little if any at the top. With his design, current is more evenly
> distributed.
>
> To avoid suggestions that saltwater, not his design, was
> the magic, another 46-foot prototype followed, built on
> rock. It offered 80 to 100 percent of the efficiency of an antenna three
> times its size.
>
> About three years ago, the University of Rhode Island
> became interested enough in Mr. Vincent's work that it gave
> him office space. After a review by engineering and physics professors,
> it began the process of patenting and selling the technology. Mr.
> Vincent has turned over all his rights to the university.
>
> "We've seen test data from Rob Vincent and it sure is attractive," said
> Quentin Turtle, the director of industry research and technology
> transfer for the university.
>
> Mr. Straw of the radio relay league said he was impressed
> with Mr. Vincent's work ethic. "But I remain somewhat skeptical,'' he
> said. "I'd like to see some validated field test measurements."
>
> Mr. Vincent said he was aware that would-be buyers of his technology
> would demand better test results, although measuring the efficiency of
> antennas is difficult. But given the scrutiny his project has received
> to date, he said he was confident that his antennas would pass muster.
>
> "I'm part of the technical staff to a whole bunch of
> Ph.D's," he said. "You can't fool these people."
>
> http://www.nytimes.com/2004/06/10/technology/circuits/10next.html?ex=108
> 7881744&ei=1&en=09fb214d67020e08
>