Here’s a problem: Tiny antennas for big wavelengths. Normally an antenna needs to be at least one-half the size of the signal wavelength it’s intended to send or receive. For example, if the wavelength is 300 MHz, the antenna should be about a half meter wide. So, how do you make much smaller antennas match big wavelengths? By having clever designs that make use of materials constructed with special properties (metamaterials) to capture or augment a radio signal.
In this case a team of researchers from the National Institute of Standards and Technology (NIST, Colorado, USA), Boeing Research & Technology (Seattle, USA), and the University of Arizona (Tucson, USA) developed an antenna only 65 mm on a side. The top surface is a copper sheet on which is printed the metal antenna circuitry. The key piece is a so-called “Z element” on the back of the copper sheet – a Z-shaped strip of copper metamaterial with an electro-magnetic inductor at the center. This catches, stores, and re-radiates the signal that normally would be lost through reflection in such a small antenna.
One of the side benefits of using the ‘metamaterial’ Z element is that it can be ‘tuned’ to handle a variety of wavelengths (frequencies). Such flexibility in a small device has many advantages. It also indicates that as the size of the antenna continues to shrink, it will still scale well against the various wavelengths needed for applications.
“The purpose of an antenna is to launch energy into free space,” explains NIST engineer Christopher Holloway, “But the problem with antennas that are very small compared to the wavelength is that most of the signal just gets reflected back to the source. The metamaterial makes the antenna behave as if it were much larger than it really is, because the antenna structure stores energy and re-radiates it.” Conventional antenna designs, Holloway says, achieve a similar effect by adding bulky “matching network” components to boost efficiency, but the metamaterial system can be made much smaller. Even more intriguing, Holloway says, “these metamaterials are much more ‘frequency agile.’ It’s possible we could tune them to work at any frequency we want, on the fly,” to a degree not possible with conventional designs.
It’s no surprise that the details of the metamaterials nor the electronics involved are not disclosed. This sort of miniaturization usually has its first use in military and intelligence applications. (The spooks get it first.)