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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