30 November 2011—Since 2008, frequent fliers have relished the luxury of on-board Internet connections. Service today relies on a fixed antenna that picks up signals from a nationwide network of cell towers. But that method offers low bandwidth at sometimes ridiculous prices. New antennas based on metamaterials, though, may soon rescue Web-addicted travelers from expensive connections in the air and elsewhere, and a group at the patent-licensing firm Intellectual Ventures (IV) thinks that it can implement the new technology by 2014.
Ideally, airlines would be able to direct dynamic antennas straight up at satellites, which is possible in one of two ways: mechanically, with a gimbal that points a dish antenna to the right part of the sky, or with a phased array, a complicated setup that electronically directs a beam by pulsing individual elements of an array in precise patterns. But mechanical gimbals are not exactly aerodynamic—one example is that massive protuberance on the nose of Predator drones. And the many phase shifters needed for phased arrays make them extremely expensive—about US $1 million a pop.
With options like these, companies like Boeing are itching for a low-cost, low-power, electronically scanned array, a technology that IV’s metamaterials researcher Nathan Kundtz calls “the holy grail of antenna design.”
The group at IV has developed a thin, lightweight antenna that takes advantage of metamaterials—synthetic substances that are being researched for use with invisibility cloaks, among other things. While natural substances derive their electromagnetic properties from their atomic composition, metamaterials gain theirs from fine, deliberately designed internal structures, which, though larger than atoms, exist on a smaller scale than the wavelengths of light they manipulate.
“Using metasurfaces for antennas is very similar to the concept used in cloaking,” says IEEE Fellow Stefano Maci, a professor of electromagnetics at the University of Siena, in Italy, who was not involved in the IV product but is working on a similar metamaterials-based antenna for the European Space Agency. The subwavelength features of metamaterials produce electromagnetic properties not found in nature, bending optical and radio waves in ways once thought to be impossible. Metamaterial cloaking devices work by refracting light around an object, and the same wave-bending concepts can be used to steer beams from antennas.
The idea of a metamaterials-based antenna isn’t new. Researchers have been working on it pretty much since metamaterials were discovered by Sir John Pendry at Imperial College London in 1999. They’re already found in some cellphones and wireless routers, which use their small size and range-boosting ability to great effect. They’re also cheap: Metamaterial elements can be easily printed using standard lithographic techniques.
The concept of a broadband metamaterial antenna is fairly straightforward. A radio wave propagates along the surface of low-loss circuit board material that’s printed with hundreds or thousands of individual metamaterial elements. Each of those elements can be tuned to resonate at a specific frequency and to direct radiation. As the surface wave passes beneath the elements, waves of radiation emit from the surface at different angles depending on how each individual element is tuned, bypassing the need for expensive phase shifters. Constructive and destructive interference between those waves of radiation produces a beam in the direction and shape desired [see video].
Today the real problem isn’t constructing those antennas—that’s been done many times over. “The most difficult step is to reconfigure and maintain a good shape of the beam over the bandwidth,” says Maci. That’s important on a bucking plane—or train or automobile—that needs to keep in constant contact with a satellite. In order to fluidly redirect a beam, the frequency and direction of each individual element on the antenna needs to be controlled on the fly.
There are a number of different ways that the metamaterial elements’ properties can be changed, says Kundtz. “In the nascent stages of the project, we outlined about 10 different ways we could change a cell’s properties,” he says, including ferroelectric materials, MEMS devices, and liquid crystals. IV won’t disclose what it has settled on yet. “We found a very inexpensive way of tuning each one of those elements,” says Russell Hannigan, director of business development at IV. “By applying a voltage across [an element], you can scatter energy whatever way you want to across the surface.”
Antenna researchers express some disbelief at IV’s claims: In just two years, the company professes to have achieved a degree of reconfigurability that others have struggled with for much longer. Maci says that he’s skeptical of the group’s work without further evidence of their methods. “In principle, it is possible to achieve what they claim; I’m working on it myself,” he says. “But it’s extremely difficult to do.”
Before the IV researchers came up with their technique, a group at HRL Laboratories led by IEEE Fellow Daniel Sievenpiper, now at the University of California, San Diego, developed an antenna whose metamaterial elements were controlled by “varactors”—diodes with variable capacitance—at nodes between them. “While more research and development is needed to achieve the performance of today’s phased-array technology for electronic beam steering, our initial data provides an indication of what could be possible,” writes Joe Colburn, director of antenna research at HRL, in an e-mail.
IV’s metamaterials antenna isn’t yet ready for production. The researchers first demonstrated two-dimensional steering only this June, and they’re aiming to have something commercially available by late 2014. Before then, they’ll have to improve the efficiency of their antenna. “Historically, efficiency is one of the banes of metamaterials,” says Kundtz. “They tend to suck up a lot of energy.”
But that should be a surmountable obstacle. Says Maci: “I believe this will be the future of reconfigurable antennas.”
This article appeared in January 2012 print as "Metamaterials Make for a Broadband Breakthrough."
This article was updated on 20 December 2011.