TECHNOLOGY AREAS: Sensors

ACQUISITION PROGRAM: PMA-265, F-18 Hornet, Super Hornet and Growler

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop innovative techniques for mitigation of multipath effects on airborne anti-jam Global Positioning System (GPS) antennas

DESCRIPTION: Multipath can affect the accuracy of an airborne GPS system through either a "structure reflection" or a "ground reflection" depending on the altitude of the aircraft. When the aircraft is at high altitudes, multipath is caused primarily through reflection or diffraction of the satellite signal from scattering sources such as the wings, tail or any other large appendage of the aircraft fuselage. These multipath effects are similar to structure bounce multipath problems experienced by a ground based GPS antenna. The direction of incidence of the multipath signal would be very dependent on the location of the antenna on the aircraft and the geometry of the aircraft fuselage.

In the case of GPS receivers, using antijam (AJ) antennas (multiple elements), one can use digital beam forming to mitigate signal multipath. The state-of-the-art GPS AJ antennas use space-time adaptive processing (STAP) for suppressing interfering signals. It is well known that for the optimum performance, STAP should be applied for beam forming/null steering instead of simple null steering. STAP in beam forming/null steering mode can also be used for multipath mitigation using spatial as well as temporal discrimination. Thus, there is a need for new digital beam forming/null steering algorithms which leads to improved multipath mitigation while suppressing interfering/jamming signals. Any novel approach to this problem will be considered.

PHASE I: Determine and demonstrate technical feasibility of beamforming/null steering algorithms that mitigate multipath effects. Effect of multipath on small anti-jam GPS antennas (<5in diameter) should also be considered.

PHASE II: Design, develop and fabricate a small anti-jam GPS array (5in diameter) prototype to demonstrate mitigation of multipath effects. Implement new algorithms for the mitigation of multipath effects on airborne anti-jam GPS antenna.

PHASE III: Proceed to further develop multipath mitigation concepts for anti-jam GPS antennas transitioning the technology to current and future naval airborne platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Multipath mitigation technologies can be useful for shipboard and ground based GPS systems.

REFERENCES:
1. Any recent Institute of Navigation (ION) conference proceedings: http://www.ion.org/meetings/#gnss

2. J.R. Guerci, Space-Time Adaptive Processing for Radar. Norwood, MA: Artech House, 2003.

3. Y. Lee and S. Ganguly, "Design of a Direction Independent Uniform Scan Array," Proceedings of ION GNSS 2005, Long Beach, CA, September, 2005, p. 667.

4. R.A. Monzingo and T. W. Miller, Introduction to Adaptive Arrays. New York: Wiley-Interscience, 1980.

5. B.R. Rao, et al., "GPS Microstrip Antenna Array on a Resistivity Tapered Ground Plane for Multipath Mitigation", The MITRE Corporation, April 2000.

6. T. K. Sarkar, et al., Smart Antennas. Hoboken: Wiley-Interscience, 2003.

7. Additional information provided by TPOC to clarify the topic description:
Current antenna electronics with STAP is mainly for suppression of strong jamming signals using null steering and are not suitable for multiplath mitigation where signal strength is not strong. For optimum performance in the presence of multipath, STAP should be applied for beam forming along with null steering instead of simple null steering.

KEYWORDS: GPS; airborne antennas; multipath; antijam; signal processing; smart antennas

** TOPIC AUTHOR (TPOC) **

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