TECHNOLOGY AREAS: Air Platform, Information Systems, Sensors

ACQUISITION PROGRAM: PMA 299, MH-60R/S Multi-Mission Helicopter Program Office; ACAT ID

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OBJECTIVE: Develop advanced beamforming/nulling algorithms for GPS anti-jam antenna electronics in the presence of reflections and modulation found on rotary wing aircraft.

DESCRIPTION: Current Controlled Reception Pattern Antenna (CRPA) systems are being used with GPS receivers for electronic protection in electromagnetically challenged environments. These systems are based on simple null steering that adapts antenna weights to steer nulls along the interfering signal direction with no constraint on the antenna response in the direction of a satellite signal. To improve the GPS navigational solution and satellite availability, future GPS CRPA systems will be beamforming and null steering. In these systems interfering signals are nulled while the antenna response is constrained in the direction of individual satellite directions. When these adaptive antenna weighting algorithms are used, navigational accuracy is achieved at the expense of greater complexity in the antenna electronics. These algorithms have been developed for antenna installation on fixed wing aircraft and have not been developed or studied on rotary wing aircraft. A rotary wing aircraft presents a more challenging radio frequency (RF) environment than the fixed wing aircraft where both the rotor blade modulation and reflection may affect the algorithms. The performance of these adaptive algorithms for GPS antenna systems mounted on rotary aircraft is unknown and needs to be carefully investigated. Also, rotary wing mounted CRPA antennas may be significantly smaller than those used on fixed wing platforms and should also be considered when evaluating candidate algorithms. Innovative adaptive weighting algorithms are being sought to reduce antenna induced phase biases in GPS code and carrier phase measurements in the rotary wing environment.

PHASE I: Determine the feasibility of developing advanced beamforming/null steering algorithms that maintain or improve navigation accuracy in the presence of rotor blade jammer reflection and modulation of GPS satellite signals.

PHASE II: Develop and demonstrate candidate algorithms and constraints. Demonstrate the candidate algorithms with current seven element GPS antennas and a model or a representative platform such as the Navy�s H-60 aircraft. Candidate algorithms should also be demonstrated with a smaller GPS antenna with fewer than seven elements.

PHASE III: Develop the electronics for transitioning the technology to current and future rotary wing naval platforms such as the Navy�s H-60 aircraft.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Technology developed under this effort will have potential applications to commercial manned and unmanned air vehicles, where varying reflections and modulation can occur.

REFERENCES:
1. McGraw, G.A., McDowell, C. & Kelly, J.M. (2006). GPS anti-jam antenna system measurement error characterization and compensation, Proceedings of ION 2006 GNSS Meeting, Fort Worth, TX

2. De Lorenzo, D. S. (2007). Navigation accuracy and interference rejection for GPS adaptive antenna arrays, Ph.D. Dissertation, Stanford University

3. O�Brien, A. & Gupta, I.J. (2008). Optimum adaptive filtering for GNSS antenna arrays. Proceedings of ION 2008 GNSS Meeting, Savannah, GA

KEYWORDS: Global Positioning System (GPS); antenna electronics; algorithms; rotor craft; anti-jam; beamforming

** TOPIC AUTHOR (TPOC) **

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