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The Army is moving closer to fielding its first mounted Anti-Jam
Antenna System, or AJAS, designed to protect GPS from adversarial
interference.
To support this effort, the U.S. Army Materiel
Command's Communications Electronics Research, Development and
Engineering Center, or CERDEC, conducts virtual, lab and live
antenna testing on behalf of Direct Reporting Program Manager
Position, Navigation and Timing, or PNT. PM PNT will use the results
to help inform the development of the antenna's specifications for
procurement.
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October 4, 2016 - Mohamed Khalil, CERDEC S&TCD, installs an anti-jam
antenna onto a Stryker vehicle inside CERDEC's Anechoic Chamber. The
chamber absorbs sound and electromagnetic waves and is used to test
a variety of frequencies for large and mobile vehicle-mounted
projects. (U.S. Army photo by Lindsey Rash, CERDEC CP&ID)
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“We are leveraging our years of expertise to ensure the
Army's PNT capabilities are adequately protected from
commercially available jammers,” said Paul Olson, chief
engineer for CERDEC's Command, Power and Integration
Directorate's Positioning, Navigation and Timing Division,
or CP&I PNTD.
The Army developed the Assured PNT
initiative to provide Soldiers with accurate and trusted
time and position information throughout their missions,
even if GPS is degraded or denied; therefore, protecting the
satellite signal is key for Soldier situational awareness,
Olson said
GPS is susceptible to jamming because the signal travels
12,000 miles from the satellite to Earth causing weak signal
power susceptible to interference by unfriendly sources.
"Jamming occurs when the signals from the GPS satellites
are overpowered by ‘noise,' and as a result, the receiver
cannot acquire those signals or calculate its position,"
said Patrick Pitoscia, lead engineer for anti-jam antennas
under CP&I PNTD. “Envision being in a crowd of people whose
voices are so loud that you can't even hear yourself speak;
the crowd in this case is the jammer.”
Anti-jam
antennas, which are comprised of an array of antenna
elements inside a radome enclosure, actively cancel out the
interference or noise created by the jammer.
“If we
go back to the crowd analogy and envision noise coming at
your left ear, your response would be to cover that ear and
use your right ear to hear the other person's voice,”
Pitoscia said. “This act produces a null in the direction of
a noise source, at which point the null cancels out the
noise and allows the good signals to come in.”
CERDEC's Space and Terrestrial Communications Directorate's,
or S&TCD's, Radio Frequency Modeling & Simulation, or M&S,
team uses electromagnetic M&S to determine antenna
placement.
“Due to time and budgetary restrictions,
engineers can only test a limited number of vehicles,” said
George Palafox, CERDEC S&TCD RF M&S branch chief. “We can
model and run the simulations expeditiously to predict how
these antennas will operate when they are mounted on
vehicles, which allows us to determine where it makes the
most sense to place the antennas while saving on testing
costs.”
CERDEC is also testing anti-jam antennas
using its Anechoic Chamber, which is filled with thousands
of carbon-filled cones that absorb sound and wavelengths
emitting from the antennas. Engineers calculated and placed
several antenna masts to replicate a true GPS constellation
– the collective group of satellites that enable GPS. The
center of the constellation features a receiver and
tripod-mounted anti-jam antenna.
“We turned on the
constellation to see if the receiver could acquire GPS to
give us position location in a friendly environment,” said
Mohamed Khalil, CERDEC S&TCD Antenna Research and Analysis
Branch team lead. “Once we proved the signal worked, we sent
out interference to jam the signal, which allowed us to
determine if the technology inside the anti-jam antenna
could null out the jamming signal and only receive the GPS
satellite signal.”
The follow-on test featured a
Stryker vehicle inside the chamber allowing engineers to
attach and systematically test each antenna's performance
following a jamming act.
CERDEC engineers
collaborated with the Navy and Air Force to learn more about
their existing anti-jam capabilities; however, the knowledge
gleaned from these partnerships could only partially inform
the Army's anti-jam antenna requirements.
“Integrating anti-jam antennas onto vehicles versus ships or
airplanes provides unique challenges,” Khalil said. “First,
we have a much smaller surface area to work with. Second, we
must contend with the electronic interference emitted by
communications antennas – either from the same vehicle or
vehicles in the vicinity.”
CERDEC will introduce a
multiple vehicle scenario next year during live testing in
an operational environment and will intentionally jam the
GPS signal to test the signal's integrity as it competes
with multiple communications systems and other operational
environment obstructions.
Future anti-jam antennas
will extend the capability from mounted platforms to the
dismounted Soldier. CERDEC and the Army Research Lab are
working together to explore smaller, more flexible antennas
that could be sewn into Soldier's uniforms and still meet
critical size, weight, and power requirements.
“Our
organization is committed to bringing Assured PNT to
Soldiers for improved situational awareness,” Olson said.
“Our comprehensive anti-jam antenna evaluations will result
in an effective capability against those whose goal is
interfere with the mission-critical GPS signal.”
By Kathryn Bailey, U.S. Army Research, Development and Engineering Command
Provided
through DVIDS
Copyright 2016
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