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].