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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

g

lltlftlte

0

1t

tf ee

2

1

l

ggckt

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