Elektor magazine had a news report on these antennas.

"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.

* 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.