"Engineered metamaterials enable remarkably small antennas"

Check this out. Although the experiments were, um, conducted at UHF, I
wonder if this development will have any implications for future HF
antennas, especially for those who have to live with CC&R's!

http://www.physorg.com/news183753164.html

The text is provided below.

Howard N7SO

NIST engineers are working with scientists from the University of Arizona
(Tucson) and Boeing Research & Technology (Seattle, Wash.) to design
antennas incorporating metamaterials—materials engineered with novel, often
microscopic, structures to produce unusual properties. The new antennas
radiate as much as 95 percent of an input radio signal and yet defy normal
design parameters. Standard antennas need to be at least half the size of
the signal wavelength to operate efficiently; at 300 MHz, for instance, an
antenna would need to be half a meter long. The experimental antennas are as
small as one-fiftieth of a wavelength and could shrink further.

In their latest prototype device, the research team used a metal wire
antenna printed on a small square of copper measuring less than 65
millimeters on a side. The antenna is wired to a signal source. Mounted on
the back of the square is a "Z element" that acts as a metamaterial—a
Z-shaped strip of copper with an inductor (a device that stores energy
magnetically) in the center (see photo).

"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.

The Z antennas were designed at the University of Arizona and fabricated and
partially measured at Boeing Research & Technology. The power efficiency
measurements were carried out at NIST laboratories in Boulder, Colo. The
ongoing research is sponsored by the Defense Advanced Research Projects
Agency.


More information: R.W. Ziolkowski, P. Jin, J.A. Nielsen, M.H. Tanielian and
C.L. Holloway. Design and experimental verification of Z antennas at UHF
frequencies. IEEE Antennas Wireless Propag. Lett., 2009 vol. 8, pp.
1329-1332


Provided by National Institute of Standards and Technology (NIST)