GPS Anti-Jam: A Simple Method of Single Antenna Null-Steering for Aerial Applications

Emily McMilin, David S. De Lorenzo, Thomas Lee, Per Enge, Dennis Akos, Stefano Caizzone, Andriy Konovaltsev

Abstract:	In this paper we introduce a backward compatible single antenna design for GPS jam mitigation on aircraft. Similar to our prior work in spoof detection [1], this anti-jam antenna requires no additional signal processing at the receiver, and it fits into the form-factor of a standard GPS antenna. There are two primary modes of operation. During the default mode, the antenna performs comparable to standard GPS antennas. During the jam mitigation mode, null steering toward the optimal azimuthal direction will generally provide greater than 10 dB of broadband signal suppression from the antenna horizon to an elevation angle about 45? below the horizon, along that azimuthal 2-D cut. Most antenna systems that provide such broadband and wide angle jam suppression, rely on multi-antenna structures that span over a wavelengths in size, permitting the simultaneous reception of a single incident waveform at multiple phase fronts. These received signals are phase coherent components of the incident waveform. With the insertion of the appropriate phase shift, they can be combined to obtain constructive and destructive interference, thus steering the array’s radiation beam or null in the desired direction, as can be seen schematically in Fig. 1a. In fact, our proposed antenna is very similar. However, instead of introducing new dedicated antenna infrastructure, we reuse the (already very necessary) body of the airplane fuselage. Specifically, the conductive body of the airplane will permit the simultaneous reception of the single incident waveform at multiple phase fronts, as can be seen in Fig. 1b. However, instead of the received signals terminating at the receive ports of a multi-antenna array, the signals received by the body of the aircraft will induce surface currents on the exterior of the aircraft, some of which will eventually reach the antenna. Our proposed antenna design will permit the reception of two signals that are phase coherent components of a single incident waveform, when that waveform is originating from below the airplane’s horizon. Similar to the concept of a large multiantenna system, with the insertion of the appropriate phase shift, the signals can be combined to obtain destructive in terference, steering a radiation null in the desired direction. Note, that this technique applies to waveforms (of any arbitrary polarization) that are originating from beneath the horizon of the aircraft, and as such, they are deemed undesirable signals that we wish to nullify. Waveforms originating from above the horizon of the aircraft are largely unaffected by this technique.
Published in:	Proceedings of the ION 2015 Pacific PNT Meeting April 20 - 23, 2015 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	470 - 483
Cite this article:	McMilin, Emily, De Lorenzo, David S., Lee, Thomas, Enge, Per, Akos, Dennis, Caizzone, Stefano, Konovaltsev, Andriy, "GPS Anti-Jam: A Simple Method of Single Antenna Null-Steering for Aerial Applications," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 470-483.
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