This is a 3D rendering of a metamaterial-lined feed horn antenna with low loss, low weight and over an octave bandwidth for satellite communications shown with satellite. Credit: Penn State |
Cheaper, lighter, and more energy-efficient
broadband devices on communications satellites may be possible using
metamaterials to modify horn antennas, according to engineers from Penn State
and Lockheed Martin Corp.
“Existing horn antennas have adequate
performance, but have undergone little change over several decades except for
advances in more accurate modeling techniques,” said Erik Lier, technical
Fellow, Lockheed Martin Space Systems Co. “Modifications enabled by
metamaterials can either enhance performance, or they can lower the mass and
thus lower the cost of putting the antenna in space.”
Lighter antennas cost less to boost into space and
more energy-efficient antennas can reduce the size of storage batteries and
solar cells, which also reduces the mass.
Metamaterials derive their unusual properties from
structure rather than composition and possess exotic properties not usually
found in nature.
“Working with Penn State,
we decided that the first year we were going focus on applications for radio
frequency antennas, where we thought we had a reasonable chance to
succeed,” said Lier.
According to Douglas H. Werner, professor of
electrical engineering, Penn
State, this is one of the
first practical implementations of electromagnetic metamaterials that makes a
real world device better.
“These results also help lay to rest the
widely held viewpoint that metamaterials are primarily an academic curiosity
and, due to their narrow bandwidth and relatively high loss, will never find
their way into real-world devices,” the researchers report in the current
issue of Nature Materials.
Wire grid metamaterial with low loss and a low refractive index (between 0 and 1) is used to line horn antennas for satellite communications. Credit: Penn State |
They specifically designed their electromagnetic
metamaterials to avoid previous limitations of narrow bandwidth and high
intrinsic material loss, which results in signal loss. Their aim was not to
design theoretical metamaterial-enhanced antennas, but to build a working
prototype.
“We have developed design optimization tools
that can be employed to meet real device requirements,” said Werner.
“We can optimize the metamaterial to get the best device performance by
tailoring its properties across a desired bandwidth to meet the specific needs
of the horn antenna.”
The researchers wanted an antenna that could work
over a broad band of frequencies—at least an octave—and improve upon existing
antennas. An octave in the radio frequency spectrum is a stretch of bandwidth
where the upper frequency is twice the lower frequency—3.5 to 7 gigahertz for
example, which is wider than the standard C-band.
Horn antennas are part of communications satellites
that relay television and radio signals, telephone calls and data around the
world. Two commonly used microwave bands on satellites are C-band—used for
long-distance radio and telecommunications—and Ku-band—used for broadcast
television and remote television uplinks.
The researchers, who also included Qi Wu and
Jeremy A. Bossard, postdoctoral fellows in electrical engineering, and Clinton
P. Scarborough, graduate student, electrical engineering, all from Penn State,
designed horn antenna liners from metamaterials with special low-index
electromagnetic properties—effective refractive index between zero and one—which
do not physically exist in natural materials. To increase bandwidth and
decrease loss, the antenna liners needed to have repetitive structure
considerably smaller than the wavelengths the antenna is designed to transmit.
Ku-band—12 to 18 gigahertz—antennas require small
structural intervals that are easily fabricated using conventional printed
circuit board manufacturing techniques, while super extended C-band—3.4 to
6.725 gigahertz—could be achieved with a simple wire grid structure that is
easily manufactured with an interval of about a quarter of an inch between
wires. The researchers chose to convert the C-band application into a
prototype.
“This is just an example of what we can do,” said Lier. “It
opens up the way for a broader range of other applications and is proof of the
new metamaterial technology and an example of how it can be used.”
