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Anti-Jam Antennas Deliver A Counter-Punch To GPS Jamming Actions
by Kathryn Bailey, U.S. Army Research, Development and Engineering Command
December 14, 2016

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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.

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)
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)

“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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