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Modeling GPS Adaptive Nulling Receivers
Ken Sherman (Satellite Software),
Haroon Rashid (AGI), Trevor Stief (AGI)
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Satellite Software
• AGI business partner specializing in antennas• Develops antenna modeling software (SATSOFT)• Developing a series of antenna plug-ins for stk &
ntk• www.satsoft.com • Contact Ken Sherman (sales at satsoft dot com)
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Overview
• Plug-In Architecture• Array Design• PA GUI• Nulling Algorithms• Null Formation• Scenarios• Results• Future Work• Conclusions
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Antenna Plug-In Architecture
stk GUI Panel
2D/3D Contours
Link Analysis &
Reports
Receivers, Transmitters & Jammers
Plug-In GUI
Antenna Geometry
Analysis & Pattern
Computation
Antenna Beamformer
Pattern Contours
Pattern Cuts
STK
Plug-In
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Wide Range of Antennas Supported by Plug-In
• Active & passive receiving antennas• Active & passive transmitting antennas• Beam steering and nulling• Arbitrary polarization (LP, CP, etc)
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Active Receiving Antenna
L1 L2 LrF1, G1
Lossless Antenna
Equivalent Active Antenna Receiver
01
1201101 )1()1()1( t
glltlftlte
0
1ttf e
e 2
1
lggckt
1
,,l
gg losslessa
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Features of Phased Array Plug In• Quickly design arrays for any receiver or transmitter in stk &
ntk
• Planar, linear, and cylindrical (conformal) array geometries
• Circular, elliptical, and polygonal apertures
• Shaped beam phase and/or amplitude synthesis
• Adaptive nulling
• Taylor circular, rectangular, and Baylis low sidelobe aperture tapers
• Several element models
• Linear & circular polarization
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Designing & Analyze the Array
Define:• Size & shape of aperture• Number & position of elements• Type of radiating elements• Nulling algorithm, if any
Perform:• Static pattern analysis
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Phased Array User Interface
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Adaptive Nulling Algorithms
• LMS steepest descent• Howells-Applebaum• Sample Covariance Matrix Inversion
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Forming a Pattern Null
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STK Scenarios
• SATCOM Link with Jammer on Airplane• GPS receiver with single jammer
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Un-Adapted Pattern
18.77
-1
-2
-3-5
-10
-20 -20
-20
-20
-20
-20
-20 -20
-20
-20
-20 -20 -30
-30
-30
-30
-30-30-30
-30
-30
-30
-30
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Adapted Pattern
16.85
-1-2
-3-5
-10
-10
-20-20
-20
-20
-20
-20-20-20-20
-20
-20
-20 -30 -30
-30
-30-30
-30
-30
-30
-30-30
-30
-30
-30
-30-30
Jammer
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3D Antenna Pattern
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Future Work
• Phased array digital beamformer• Phased array interface to future stk/radar module• Reflector model (physical optics)• Wire antenna model (moment method)• Scripting (nulling algorithms, etc)
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Conclusions
• Flexible antenna plug-in architecture for stk & ntk• New phased array plug-in under development• Improvement of s/n by nulling a jammer• Future work
Challenges:• Accurate gain = pattern integration = cpu time• Providing visual feedback• Easy-to-use but comprehensive GUI
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