Why Mobile Phones Can Do So Many Things: The Invention Of The Fractal Antenna

By Robert Colburn, IEEE History Center

[EDITOR’S NOTE: This article originally appeared in IEEE-USA InSight. It is reprinted here with permission from IEEE-USA. Copyright 2021 IEEE.] Mobile phones perform multiple tasks by transmitting and receiving on many different frequencies. For example, when the user first dials, there is a carrier frequency that the phone and the base station communicate with each other to set up the call, establish which cell tower the phone is in range of, and choose which frequency or frequencies to use for the call. Some mobile phone systems use frequency-shift keying, which means the zeros of the digital signal are sent on one frequency and the ones are sent on another. BlueTooth, WiFi, and other applications use yet more frequencies. Prior to the late 1980s, this would have required mobile phones to use an antenna for each frequency. Mobile phones would have needed many different antennas sticking out, each sized according to wavelength. Instead, today’s mobile phones owe their sleek design in part to antennas whose shapes are determined by fractals. In 1982, mathematician Benoit Mandelbrot published his influential book, The Fractal Geometry of Nature. Some of the earliest applications of fractals were in computer graphics. Mandelbrot gave a paper on the landscapes of an imaginary planet at the 99th Colloquium of the International Astronomical Union, held in Balaton, Hungary in June of 1987. Also giving a paper at the conference was IEEE member and radio astronomer Prof. Nathan Cohen of Boston University. Cohen was a ham radio operator, and Mandelbrot’s talk intrigued him. He wondered how an antenna shaped according to fractal geometry would work. Cohen found that it worked very well. However, his then landlord had a strict policy about not attaching antennas to the building. Cohen was working with 2-meter FM, meaning that a conventional antenna would need to be about one meter, and thus quite visible. Having found that his fractal antennas could be made much smaller, Cohen made a fractal microstrip antenna out

Scaled up example of an enhanced RCS road reflector for autonomous cars/roads. (Courtesy © Fractal Antenna Systems, Inc.)

(left) Fractal antennas as metamaterials (showing insides) for far smaller replacement of a Yagi-Uda antenna. and (right) 2.4 GHz metablateTM antenna and the Yagi-Uda it replaces. (Courtesy © Fractal Antenna Systems, Inc.)

of aluminum foil, glue, and construction paper using the pagoda motif, and attached it to the railing of his apartment. It was about six inches square. Despite its diminutive size and looking more like a doily than an antenna, (as well as being up on the 27th floor), the landlord learned of its existence and cut it down while Cohen was at work, teaching a math class. Cohen found its sad remains in the snow on the ground below a few days later. Given that the antenna’s descendants now function in hundreds of millions of devices around the world, the severing of the prototype must surely rank as one of the most infelicitous acts of technological obstruction since the Visigoths dismantled the Roman aqueducts. In addition to their uses in mobile phones and computers, fractal antennas have important applications in RFIDs and in vehicular radar and collision-avoidance systems. They reduce scattering of the signal and enhance the radar reflection of highway tags. As one measure of fractal antennas’ importance, IEEE has published more than 2,100 papers on them. “Fractal antennas not only shrink antenna sizes, but also control multiband performance, enable wideband use, and actually increase realized gain in small sizes. The gain attribute arises from being able to produce multiple current maxima, such as on a fractal perimeter, in a highly compact area. Constructive interference can happen in regimes far smaller than a ¼ wave,” Cohen explains. Fractal Antenna Systems, the company Cohen founded, filed U.S. patent 6,452,553 in August of 1995 for the fractal antenna. The earliest adopters of the technology were government customers. “Today,” notes Cohen, “you would be challenged to get an x-ray, use radios or phones in a public building, or fly on a commercial jet without fractal antennas. Fractals are a big part of keeping the world connected.” In addition to being a very widely used technology, fractal antennas are visually intricate and beautiful. Because they are small enough to be hidden inside the technologies that they make work, most of us are not aware of them. The author hopes that this article has raised their visibility.

SOURCE

Robert Colburn, IEEE-USA Insight, IEEE History Center, Aug. 4, 2021, https://insight.ieeeusa.org/articles/whymobile-phones-can-do-so-many-things-the-invention-of-thefractal-antenna/.

ABOUT THE AUTHOR

Robert Colburn is the research coordinator at the IEEE History Center. For more articles by the History Center staff, visit their publications page at: http:// ethw.org/Archives:Books_and_Archival_ Publications or visit the IEEE History Center’s Web page at: http://www.ieee. org/about/history_center/index.html. The IEEE History Center is partially funded by donations to the History Fund of the IEEE Foundation.

100th Anniversary Celebration of the First Trans-Atlantic Radio Transmission of a Message by Amateur Radio Saturday, December 11, 2021

HISTORY WAS MADE -- On a cold winter night on December 11, 1921, members of the Radio Club of America sent the first amateur radio message from a small shack in Greenwich, CT that was received by American Paul Godley in Ardrossan, Scotland. This transatlantic test proved the value of shorter wavelengths – long considered worthless to long distance communications and through their success ushered in the age of global shortwave radio communications.

C CELEBRATIONS -- The Antique Wireless Association, in association with the Vintage Radio and Communications Museum of Connecticut in Windsor, CT, the Radio Club of America, the American Radio Relay League, and the Radio Society of Great Britain, will participate in the 100th Anniversary special events to be held Saturday, December 11, 2021.

R REPLICA TRANSMITTER -- For the 75th anniversary celebration of the 1BCG accomplishment in 1996, AWA members Bob and Mike Raide constructed a replica of the 1921 transmitter. For this 100th celebration, AWA Museum Staff has restored the replica. AWA will place the replica 1BCG transmitter on display at the VRCMCT Museum Saturday afternoon, December 11, 2021. The Museum will be open to the public.

OPERATION & DISPLAY -- The Vintage Radio and Communications Museum of Connecticut in Windsor CT has graciously offered to host AWA operation of the replica transmitter during the evening of December 11th. “AWA sincerely appreciates the support and commitment of VRCMCT Museum and Museum Staff to make this 100th anniversary celebration use of the AWA replica transmitter possible,” said Robert Hobday N2EVG, AWA President and Chairman.

The transmitter will be operating as W2AN/1BCG on 1.820 MHz, plus or minus, using CW. Members of the RSGB in Ardrossan will be listening for those signals with the goal of replicating the 1921 successful transatlantic reception using a 1921 designed transmitter. The 1921 message was sent one-way. Acknowledgment of Paul Godley’s reception of 1BCG’s massage was sent back to the US via telegraph to Wales and the Marconi high power radio transmitter in Wales. The VRCMCT Museum will be open to the public to view the evening operation of the 1BCG replica transmitter.

I INFORMATION -- For further details on the operating schedule and the history of the accomplishment in 1921, please visit the AWA 1BCG.org website.

C CERTIFICATES -- Any station receiving the 100th centennial message sent by W2AN/1BCG can receive a 100th 1BCG Anniversary Certificate emailed from AWA by emailing their report to 1BCG@AntiqueWireless.org.