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GNSS Antenna Arrays for Situational Awareness


OBJECTIVE: Develop multi-platform Global Navigation Satellite System (GNSS) antenna array capabilities for situational awareness (SA), providing direction finding and geo-location of the GNSS signals. DESCRIPTION: Single element and co-located multi-element antennas are being developed to receive navigation signals in the GNSS frequency band, covering the GPS, GLONASS, GALILEO, and COMPASS navigation systems. This next generation GNSS user equipment must be capable of operating in an electronically challenging environment and providing situational awareness of this environment to enhance mission planning and weapon system effectiveness. Multi-element antenna arrays are of particular interest for next generation GNSS systems, since they can provide both the anti-jam (A/J) and situational awareness (SA) capabilities that are required for operation in these environments. Direction finding and geo-location of GNSS signals for SA is the primary focus of this SBIR topic. Although A/J GPS capability is desirable (Reference 1), it is not a requirement for this effort. Direction finding (DF) algorithms that are used with arrays of antenna elements are well-established, Reference 2, and their use in geo-location of GPS signals has been demonstrated, Reference 3. More recently, a ground-based operational prototype system targeted to GNSS interference source detection and localization was demonstrated, Reference 4. This system was implemented with a spatially distributed array of sensor nodes and was capable of simultaneous localization of multiple emitters. This SBIR topic seeks to expand on these previous efforts by developing multi-element antenna arrays for both manned and unmanned air vehicles that cover the full GNSS band and that can provide SA capabilities, while meeting the size, weight, power and cost constraints of these vehicles. There are three critical aspects in designing capabilities for this type of antenna array: a) antenna elements that cover the full GNSS frequency band (1160 - 1600 MHz) with sufficient gain, bandwidth and radiation pattern stability to perform the SA function, while at the same time minimizing cost, size, and weight; b) simple connectivity of the data from the antenna elements to a central processor; and c) robust SA algorithms. This SBIR should concentrate on novel technologies for the multi-band elements, array configuration and connectivity (a and b), while utilizing generic processing algorithms for the SA processing (c), with the goal to indicate the robustness of the design over the GNSS frequency band. Alternative element designs and array configurations should be studied under this effort to accommodate integration into a range of different sized air vehicles, from smaller unmanned air vehicles to larger aircraft, such as the F-16. A larger antenna array could obtain more accurate SA capability, but would increase the cost and complexity of integration into the platform. Distributing the antenna array elements across the platform could be considered, as it would result in a larger antenna, with more accurate SA capability than a single co-located multi-element antenna, but this configuration could also result in sharp variations in the pattern, which must be considered in the processing. Trade-offs in element/array size and placement, as well as cost, weight, power and processing requirements should be considered in the Phase I study. Alternatives for communications and connectivity between the elements and the central processor should also be considered in the design trade-off study. PHASE I: Develop antenna elements that cover the GNSS band and approaches for combining the elements into a networked array (using modeling, simulation, and sub-scale prototypes if possible). Show that these approaches will work over the GNSS frequency band, are technically feasible, and are reasonable with respect to size and weight for different platforms from UAV's to larger aircraft. PHASE II: Utilizing the design from Phase I, fabricate and demonstrate a prototype system that combines a number of GNSS elements into a networked array on a platform (representative ground-plane), which wirelessly communicates data to a central processor. Test the resulting system to demonstrate the combined antenna performance over the GNSS frequency band and the capability of obtaining SA information. PHASE III: Follow-on activities are expected to pursue in both military and commercial applications for schemes which network different antennas (not all with full GNSS capabilities), on and off platform, for the GNSS SA applications. REFERENCES: 1. Air Force SBIR Phase I Topic AF 083-159, Combining Remotely Located GPS Antennas on UAV Platforms, 2009. 2. Van Trees, H.L."Optimum Array Processing, Part IV"Wiley, 2002. 3. Isoz,O. A., Balaei, T. and Akos, D."Interference detection and localization in the GPS L1 band,"in Proceedings of the ION ITM, (San Diego, CA), pp. 925-929, Institute of Navigation, Jan. 2010. 4. Bhatti, J.A., Humphreys, T.E. and Ledvina, B.M.,"Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System,"2012 IEEE/ION Position Location and Navigation Symposium (PLANS), 2012. 5. Mailloux, R. J., Phased Array Antenna Handbook, Artech House, 1994.
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