1. No category

Nonlinear Effects in
Active Phased Array
System Performance
Larry Williams, PhD
Director of Product Management
ANSYS Inc.
1
© 2011 ANSYS, Inc.
April 24, 2015
Advanced Simulation
• Simulate the Complete Product
– Real-life behavior in real-world environments
– Comprehensive multiphysics
– Complete system modeling
Physical
Prototype
Concept & Design
Simulation-Driven
Product Development
Production
Simulation-Driven Product Development
Minimizes TOTAL time through the loop
Maximizes validated learning
2
© 2011 ANSYS, Inc.
April 24, 2015
Simulation Driven Product Development
• Integrating BFN with Antenna Elements for a Radar System
–
–
–
3D Antenna Array Design
3D Beam Forming Network (BFN) Design
Radar System Platform performance
Simulation-Driven
Product Development
BFN
Digital Phase Shifter/Attenuators
Power Splitter
Antenna Array
3ANSYS, Inc.©Proprietary
2014 ANSYS, Inc.
© 2009 ANSYS, Inc. All rights reserved.
April 24, 2015
Platform Performance
1-3
February 23, 2009
Inventory #002593
HFSS – Advanced Simulation Technology
Finite Element Method
FEM Transient
• Ideal for fields that change
• Efficiently handles
complex material and
geometries
•
versus space and time;
scattering locations
Local time stepping
Circuit Solver
Dynamic Link to Field Solvers
4
© 2011 ANSYS, Inc.
Integral Equations (IE)
Physical Optics(PO)
• Efficient solution
technique for open
radiating and scattering
of metallic objects
• ACA and MLFMM
• Ideal for electrically large,
April 24, 2015
conducting and smooth
objects
Multi-Scale Multi-Domain System
MIMIC in HFSS 3D Layout
3D EM Simulation of Circulator
Domains: Circuit, Frequency, Time,
FEM, IE, PO…etc
Antenna Element/Array
3D EM Simulation of Amp Package
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© 2011 ANSYS, Inc.
April 24, 2015
Scale: Circuit level, component
level, antenna and array level,
small component on large aircraft
R16 Electronics Desktop
HFSS-IE
HFSS Layout
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© 2011 ANSYS, Inc.
April 24, 2015
HFSS
Circuit
Active Phased Array
on Aircraft
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© 2011 ANSYS, Inc.
April 24, 2015
Integrated Radar System
Northrop Grumman
RQ-4 Global Hawk
Side-looking
Synthetic Aperture Radar
Radar - Operational Modes
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© 2011 ANSYS, Inc.
April 24, 2015
Integrated Antenna Performance
Goal
Understand antenna system performance in actual
operational environment
Solved!
55 minutes , 32 cores, 75GB RAM
UAV solved with HFSS-IE
Data-link: antenna array is a near
field source in HFSS-IE design
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© 2011 ANSYS, Inc.
April 24, 2015
16 x 64 Element Phased Array in HFSS
Solved!
3 hours, 16 cores, 75GB RAM
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© 2011 ANSYS, Inc.
April 24, 2015
Concept: Antenna Requirements
• Reconfigurable: Electronically Steerable Phased Array
• Phased Array
– A group of antenna elements in which the relative amplitudes and phases are
varied to construct an effective radiation pattern by constructive and destructive
interference
Amplitude
Phase
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© 2011 ANSYS, Inc.
April 24, 2015
Concept: Shaped Beam
Wide Area – Cosecant-Squared Beam
Spot Area - Taylor Weighting
Requires 16 antenna elements
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© 2011 ANSYS, Inc.
April 24, 2015
Concept: Controlling Amplitude and Phase
Transmit/Receive (T/R) Module Block Diagram
Power Distribution
Antenna Element
Beam Forming Network
(BFN)
Transmit
Circulator
Power Amplifier
Receive
(Amplitude/Phase)
Replicate
<n> Times
Component Requirements
– Phase
– 5-bit Phase Shifter
– Amplitude
– 15 dB dynamic range
– 5-bit Digital Attenuator
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© 2011 ANSYS, Inc.
April 24, 2015
Design Approach: Integrated System
Antenna + T/R
Antenna
Element
Circulator
Amp
BFN
Power
Distribution
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© 2011 ANSYS, Inc.
April 24, 2015
Radar Tx System
Beam Forming Network
Radar Tx Performance
Power Distribution
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© 2011 ANSYS, Inc.
April 24, 2015
Antenna Array
HFSS 3D Layout
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© 2011 ANSYS, Inc.
April 24, 2015
Feed Network Design
Verification
Design
Optimization
Offset
Radius
HFSS 3D Components
HFSS Circuit Optimization
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© 2011 ANSYS, Inc.
April 24, 2015
Multiscale: 3D With Embedded Circuits
3D Physical Device Model
Ideal Electrical Model
Digital Phase Shifter/Attenuators
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© 2011 ANSYS, Inc.
April 24, 2015
Transistor Based or X-Parameter Power Amplifier
Quantization Effect on Boresite Pattern
Quantized Phase/Atten
Ideal Phase/Atten
• Quantization of the element weights makes little difference in the beamwidth or
sidelobe levels
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© 2011 ANSYS, Inc.
April 24, 2015
Quantization Effect on Steered Pattern
Quantized Phase/Atten
Ideal Phase/Atten
• The difference is not noticeable near the main lobe
• Parasitic lobe near 0 degrees is the result of phase rounding quantization, and can
be eliminated with a variety of methods[1]
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© 2011 ANSYS, Inc.
April 24, 2015
M.S. Smith and Y.C. Guo, “A Comparison of Methods for Randomizing Phase Quantization
Errors in Phased Arrays,” IEEE Trans. On Ant. & Prop., v. AP-31, no. 6, Nov 1983
[1]
Nonlinear Effects on
Shaped Beam
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© 2011 ANSYS, Inc.
April 24, 2015
Z
X
XY Plot 4
Ansoft Corporation
16x1_o1
0.00
-20dB
-10.00
-30dB
-20dB
dB10normalize(GainL3Y)
-20.00
-30.00
-40.00
-50.00
-60.00
-70.00
-90.00
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© 2011 ANSYS, Inc.
-60.00
-30.00
0.00
Theta [deg]
30.00
60.00
R.S. Elliott and George J. Stern, “A New Technique for Shaped Beam
Synthesis of Equispaced Arrays,” IEEE Trans. Antennas Propagat., vol. APApril 24, 2015
32, No. 10, Oct. 1984.
90.00
Amplitude / Phase Distribution
Element Number Excitation Voltage Element Number
(m)
(Vm)
(m)
1
0.928 -36.67
9
2
0.464 -78.29
10
3
0.701 -51.58
11
4
0.728 -35.40
12
5
0.629 -26.34
13
6
0.741 -4.49
14
7
0.999 11.80
15
8
1.000 25.76
16
Excitation Voltage
(Vm)
1.083 45.42
1.444 53.23
1.547 59.33
1.564 76.21
2.096 78.29
2.581 62.38
2.087 40.67
1.524 -4.77
15.00
14.00
12.00
11.00
10.00
9.00
Amplitude (dB)
15dB Dynamic Range
13.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
0
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© 2011 ANSYS, Inc.
1
2
3
April 24, 2015
4
5
6
7
8
9
Element Number
10
11
12
13
14
15
16
17
BJT Power Amplifier is Nonlinear
L22
1e-006
0
Nexxim2
L21
I23
U1
1e-006
V24
0
U3
Nexxim4
Port1
C20
Port2
Port2
Q17
Port1
C19
Port1
1e-009
Port2
1e-009
bjt33
0
Ansoft Corporation
16.00
gain, pout, phase
Nexxim
21.00
Pout
14.00
20.00
10.00
8.00
6.00
dB(TG(Port2,Port1)<F1,F1>)
dBm(P(Port2)<F1>)
12.00
19.00
Gain
18.00
Curve Info
dBm(P(Port2)<F1>)
HB1Tone
dB(TG(Port2,Port1)<F1,F1>)
HB1Tone
17.00
4.00
16.00
2.00
0.00
15.00
-20.00
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© 2011 ANSYS, Inc.
-18.00
April 24, 2015
-16.00
-14.00
-12.00
-10.00
pin [dBm]
-8.00
-6.00
-4.00
-2.00
0.00
Gain Compression
XY Plot 3
Ansoft Corporation
PowerSweep
Gain Compression
6.00
4.00
2.00
~15dB
Y1
0.00
-2.00
-4.00
-6.00
-8.00
-10.00
-10.00
-5.00
Linear
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© 2011 ANSYS, Inc.
0.00
5.00
P1 [dBm]
10.00
+10dBm
April 24, 2015
15.00
+14dBm
20.00
Linear (blue) vs. +10dBm
XY Plot 2
Ansoft Corporation
16x1
0.00
Blue: 0dBm (linear)
Red: +10dBm
-10.00
Y1
-20.00
-30.00
-40.00
-50.00
-100.00
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© 2011 ANSYS, Inc.
-50.00
April 24, 2015
0.00
Theta [deg]
50.00
100.00
Linear (blue) vs. +14dBm
XY Plot 2
Ansoft Corporation
16x1
0.00
Blue: 0dBm (linear)
Red: +14dBm
-10.00
Y1
-20.00
-30.00
-40.00
-50.00
-100.00
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© 2011 ANSYS, Inc.
-50.00
April 24, 2015
0.00
Theta [deg]
50.00
100.00
Infinite and Finite
Planar Array
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© 2011 ANSYS, Inc.
April 24, 2015
Array Description
• 16 x64 Element Array
– 1024 Y-Polarized Quasi-Yagi Elements
• 15mm x 15mm Square Lattice
– 50o Conical Scan Volume
• Frequency Band from 9GHz to 11GHz
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© 2011 ANSYS, Inc.
April 24, 2015
Array Analysis Methods
Infinite Array
Finite Array Domain Decomposition
Unit Cell with
Periodic Boundaries
•
Provides Embedded Element Pattern
•
Predicts Blind Zones and Surface Waves
•
Assumes an infinite array
•
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• Includes mutual coupling effects
• No edge effects
• Uniformly Excited
Unit Cell
•
Solver decomposes array into domains of
“similar element type” for more efficient
solve times
• Corner elements
• Edge elements
• Center elements
•
Leverages many computers to solve large
but finite array
•
Mesh copied from unit cell
Small volume; fast simulation
© 2011 ANSYS, Inc.
April 24, 2015
Infinite Array
Mirror
Quasi-Yagi
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© 2011 ANSYS, Inc.
April 24, 2015
Mirror
antenna element
Image courtesy http://www.daviddarling.info/
Infinite Array Unit Cell
• Periodic boundary conditions
• Slave has same fields as Master but for a phase
shift
– Simulates any scan condition.
• The radiated fields are terminated through a
Floquet Port
• The scan volume can be evaluated by
parametrically sweeping the scan angle (qs,fs)
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©2013 ANSYS, Inc.
Floquet Port
Slave
Master
z
Effects on the Pattern
y
x
Element Pattern Gain calculated
directly from Floquet Transmission
Coefficients
G
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4A
2
TM
© 2011 ANSYS, Inc.
2
0, 0
 TE0,0
2
cos(q )
April 24, 2015
s
E-Plane Scan Blindness
Floquet Transmission Coefficients Indicate a
Possible Surface Wave
Transmisssion
Grating Lobe
Possible
Surface Wave
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© 2011 ANSYS, Inc.
April 24, 2015
Surface Wave Verification
• The fields at the problem
frequency and scan angle
indicate a surface wave is
the cause.
• The surface wave was
found because Floquet
Ports were used
– More frequencies could
be evaluated
– The interpolation in the
interpolating sweep
help reveal the surface
wave
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© 2011 ANSYS, Inc.
April 24, 2015
Finite Array Domain Decomposition
Method (DDM)
• Mesh copied from unit cell design to every
element in finite array design
- Reinforces periodicity of array
- Dramatically reduces mesh time
associated with finite array analysis
16x64 Array
• Solver decomposes array into domains and
solves those domains in parallel
• Full array solved with composite excitation
for significant gains in simulation speed
Import mesh
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Unit
Cell
© 2011 ANSYS, Inc.
April 24, 2015
Time (16 cores)
RAM
Unit Cell
15mins
7GB
Finite Array
3hrs
75GB
Finite Array Domain Decomposition
Method (DDM)
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© 2011 ANSYS, Inc.
April 24, 2015
Finite Array vs Infinite Array Factor
Blue: Infinite Array Factor
Red: Finite Array
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© 2011 ANSYS, Inc.
April 24, 2015
Platform Integration
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© 2011 ANSYS, Inc.
April 24, 2015
Array on UAV
UAV solved with HFSS-IE
Data-link: antenna array is a near field source in HFSS-IE design
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© 2011 ANSYS, Inc.
April 24, 2015
Time (32 cores)
RAM
55mins
75GB
Array Performance on Aircraft
Blue: Array on Aircraft
Red: Finite Array
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© 2011 ANSYS, Inc.
April 24, 2015
Multiphysics
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© 2011 ANSYS, Inc.
April 24, 2015
Electromagnetics
Physics-Based Simulation
Electronics
RF/Antenna and SI/PI/EMI
Antenna Array
Antenna Placement
Large Scale
Platform Interaction
Rotor Blade
Modulation
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© 2011 ANSYS, Inc.
Co-Site
Lightening
Strike
April 24, 2015
Physics-Based Simulation
Structural Mechanics
Coupled Solution
Electro-Mechanical
Design
Stress/
Explicit Dynamics
Rivet Fatigue
Vibration
Composites
Failure
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© 2011 ANSYS, Inc.
April 24, 2015
Physics-Based Simulation
Fluid Dynamics
Engine
Combustion
Engine
Cooling
Landing Deck
Air Flow
Rotor Design and
Aero acoustics
Aerodynamics
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© 2011 ANSYS, Inc.
April 24, 2015
Landing Gear
Turbulent Flow
Summary
• Modern simulation allows real-world system analysis
– Electromagnetics
– Mechanical
– Fluid Dynamics
• Multi-scale analysis of phased array
– Quantization effects
– Nonlinear circuit effects
• Planar array simulation
– Infinite array using periodic boundaries used to find blind zones and surface waves
– Finite array reveals pattern degradation due to array edges
• Platform Integration
– Brings all techniques together for full installed performance
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© 2011 ANSYS, Inc.
April 24, 2015
Thank You
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© 2011 ANSYS, Inc.
April 24, 2015