nonlinear effects in active phased array system performanceimapsne.net/2015...

© 2011 ANSYS, Inc. April 24, 2015 1

Nonlinear Effects in Active Phased Array System Performance

Larry Williams, PhD Director of Product Management

ANSYS Inc.

© 2011 ANSYS, Inc. April 24, 2015 2

Advanced Simulation

• Simulate the Complete Product

– Real-life behavior in real-world environments

– Comprehensive multiphysics

– Complete system modeling

Concept & Design

Physical

Prototype

Production

Simulation-Driven Product Development

Simulation-Driven Product Development Minimizes TOTAL time through the loop Maximizes validated learning

1-3 ANSYS, Inc. Proprietary

© 2009 ANSYS, Inc. All rights reserved.

February 23, 2009

Inventory #002593 © 2014 ANSYS, Inc. April 24, 2015 3

• 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

Simulation-Driven

Product Development

Antenna Array

Power Splitter

BFN

Digital Phase Shifter/Attenuators

Platform Performance

© 2011 ANSYS, Inc. April 24, 2015 4

HFSS – Advanced Simulation Technology

Finite Element Method • Efficiently handles

complex material and geometries

Integral Equations (IE) • Efficient solution

technique for open radiating and scattering of metallic objects

• ACA and MLFMM

Physical Optics(PO) • Ideal for electrically large,

conducting and smooth objects

FEM Transient • Ideal for fields that change

versus space and time; scattering locations

• Local time stepping

Circuit Solver Dynamic Link to Field Solvers

© 2011 ANSYS, Inc. April 24, 2015 5

Multi-Scale Multi-Domain System

MIMIC in HFSS 3D Layout Domains: Circuit, Frequency, Time, FEM, IE, PO…etc

Scale: Circuit level, component level, antenna and array level, small component on large aircraft

3D EM Simulation of Amp Package

3D EM Simulation of Circulator

Antenna Element/Array

© 2011 ANSYS, Inc. April 24, 2015 6

R16 Electronics Desktop

HFSS-IE

HFSS Layout

HFSS

Circuit

© 2011 ANSYS, Inc. April 24, 2015 7

Active Phased Array on Aircraft

© 2011 ANSYS, Inc. April 24, 2015 8

Integrated Radar System

Side-looking

Synthetic Aperture Radar

Northrop Grumman RQ-4 Global Hawk

Radar - Operational Modes

© 2011 ANSYS, Inc. April 24, 2015 9

Integrated Antenna Performance

UAV solved with HFSS-IE Data-link: antenna array is a near field source in HFSS-IE design

Understand antenna system performance in actual operational environment

Goal

Solved! 55 minutes , 32 cores, 75GB RAM

© 2011 ANSYS, Inc. April 24, 2015 10

16 x 64 Element Phased Array in HFSS

Solved! 3 hours, 16 cores, 75GB RAM

© 2011 ANSYS, Inc. April 24, 2015 11

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

© 2011 ANSYS, Inc. April 24, 2015 12

Concept: Shaped Beam

Wide Area – Cosecant-Squared Beam Spot Area - Taylor Weighting

Requires 16 antenna elements

© 2011 ANSYS, Inc. April 24, 2015 13

Concept: Controlling Amplitude and Phase

Power Distribution Beam Forming Network

(BFN)

(Amplitude/Phase)

Power Amplifier

Circulator

Antenna Element

Replicate

<n> Times

Transmit

Receiv

e

Transmit/Receive (T/R) Module Block Diagram

– Phase

– 5-bit Phase Shifter

– Amplitude

– 15 dB dynamic range

– 5-bit Digital Attenuator

Component Requirements

© 2011 ANSYS, Inc. April 24, 2015 14

Design Approach: Integrated System Antenna + T/R

Power

Distribution

BFN

Amp

Antenna

Element

Circulator

© 2011 ANSYS, Inc. April 24, 2015 15

Radar Tx System

Power Distribution

Beam Forming Network

Antenna Array

Radar Tx Performance

© 2011 ANSYS, Inc. April 24, 2015 16

HFSS 3D Layout

© 2011 ANSYS, Inc. April 24, 2015 17

Feed Network Design

Verification

Design Optimization

Offset Radius

HFSS 3D Components

HFSS Circuit Optimization

© 2011 ANSYS, Inc. April 24, 2015 18

Multiscale: 3D With Embedded Circuits

3D Physical Device Model

Ideal Electrical Model

Digital Phase Shifter/Attenuators Transistor Based or X-Parameter Power Amplifier

© 2011 ANSYS, Inc. April 24, 2015 19

Quantization Effect on Boresite Pattern

• Quantization of the element weights makes little difference in the beamwidth or sidelobe levels

Quantized Phase/Atten

Ideal Phase/Atten

© 2011 ANSYS, Inc. April 24, 2015 20

Quantization Effect on Steered Pattern

• 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]

[1] 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

Quantized Phase/Atten

Ideal Phase/Atten

© 2011 ANSYS, Inc. April 24, 2015 21

Nonlinear Effects on Shaped Beam

© 2011 ANSYS, Inc. April 24, 2015 22

-90.00 -60.00 -30.00 0.00 30.00 60.00 90.00Theta [deg]

-70.00

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00d

B1

0n

orm

alize

(Ga

inL

3Y

)Ansoft Corporation 16x1_o1XY Plot 4

-20dB -20dB -30dB

Z

X

R.S. Elliott and George J. Stern, “A New Technique for Shaped Beam Synthesis of Equispaced Arrays,” IEEE Trans. Antennas Propagat., vol. AP-32, No. 10, Oct. 1984.

© 2011 ANSYS, Inc. April 24, 2015 23

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Element Number

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

Am

plit

ude (

dB

)

Amplitude / Phase Distribution Element Number

(m) Excitation Voltage

(Vm) Element Number

(m) Excitation Voltage

(Vm) 1 0.928 -36.67 9 1.083 45.42 2 0.464 -78.29 10 1.444 53.23 3 0.701 -51.58 11 1.547 59.33 4 0.728 -35.40 12 1.564 76.21 5 0.629 -26.34 13 2.096 78.29 6 0.741 -4.49 14 2.581 62.38 7 0.999 11.80 15 2.087 40.67 8 1.000 25.76 16 1.524 -4.77

15

dB

Dyn

amic

Ran

ge

© 2011 ANSYS, Inc. April 24, 2015 24

BJT Power Amplifier is Nonlinear

0

0

0

Port1

Port2

Q17

bjt33

1e-009

C19 1e-009

C20

1e-0

06

L21

1e-0

06

L22

I23

V24

Port2Port1

U1Nexxim2

Port1 Port2

U3Nexxim4

-20.00 -18.00 -16.00 -14.00 -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00pin [dBm]

15.00

16.00

17.00

18.00

19.00

20.00

21.00

dB

(TG

(Po

rt2

,Po

rt1

)<F

1,F

1>

)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

dB

m(P

(Po

rt2

)<F

1>

)

Ansoft Corporation Nexximgain, pout, phase

Curve Info

dBm(P(Port2)<F1>)

HB1Tone

dB(TG(Port2,Port1)<F1,F1>)

HB1Tone

Pout

Gain

© 2011 ANSYS, Inc. April 24, 2015 25

Gain Compression

-10.00 -5.00 0.00 5.00 10.00 15.00 20.00P1 [dBm]

-10.00

-8.00

-6.00

-4.00

-2.00

0.00

2.00

4.00

6.00

Y1

Ansoft Corporation PowerSweepXY Plot 3

Linear +10dBm +14dBm

Gain Compression

~15dB

© 2011 ANSYS, Inc. April 24, 2015 26

Linear (blue) vs. +10dBm

-100.00 -50.00 0.00 50.00 100.00Theta [deg]

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

Y1

Ansoft Corporation 16x1XY Plot 2

Blue: 0dBm (linear) Red: +10dBm

© 2011 ANSYS, Inc. April 24, 2015 27

Linear (blue) vs. +14dBm

-100.00 -50.00 0.00 50.00 100.00Theta [deg]

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

Y1

Ansoft Corporation 16x1XY Plot 2

Blue: 0dBm (linear) Red: +14dBm

© 2011 ANSYS, Inc. April 24, 2015 28

Infinite and Finite Planar Array

© 2011 ANSYS, Inc. April 24, 2015 29

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

© 2011 ANSYS, Inc. April 24, 2015 30

Array Analysis Methods

Infinite Array Finite Array Domain Decomposition

Unit Cell with Periodic Boundaries

• Provides Embedded Element Pattern • Includes mutual coupling effects

• Predicts Blind Zones and Surface Waves

• Assumes an infinite array

• No edge effects • Uniformly Excited

• Small volume; fast simulation

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

© 2011 ANSYS, Inc. April 24, 2015 31

Infinite Array

Mirror Mirror

Image courtesy http://www.daviddarling.info/

Quasi-Yagi antenna element

©2013 ANSYS, Inc. 32

• 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)

Infinite Array Unit Cell

Master Slave

Floquet Port

© 2011 ANSYS, Inc. April 24, 2015 33

Effects on the Pattern

E-Plane Scan Blindness

)cos(4 2

0,0

2

0,02 sTETMA

G q

Element Pattern Gain calculated

directly from Floquet Transmission

Coefficients

x y

z

© 2011 ANSYS, Inc. April 24, 2015 34

Floquet Transmission Coefficients Indicate a Possible Surface Wave

Grating Lobe

Possible

Surface Wave

Transmisssion

© 2011 ANSYS, Inc. April 24, 2015 35

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

© 2011 ANSYS, Inc. April 24, 2015 36

• 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

• Solver decomposes array into domains and solves those domains in parallel

• Full array solved with composite excitation for significant gains in simulation speed

Finite Array Domain Decomposition Method (DDM)

Import mesh

16x64 Array

Time (16 cores) RAM

Unit Cell 15mins 7GB

Finite Array 3hrs 75GB Unit Cell

© 2011 ANSYS, Inc. April 24, 2015 38

Finite Array vs Infinite Array Factor

Blue: Infinite Array Factor Red: Finite Array

© 2011 ANSYS, Inc. April 24, 2015 40

Array on UAV

UAV solved with HFSS-IE Data-link: antenna array is a near field source in HFSS-IE design

Time (32 cores) RAM

55mins 75GB

© 2011 ANSYS, Inc. April 24, 2015 43

Physics-Based Simulation

Rotor Blade

Modulation

Large Scale

Platform Interaction

Electromagnetics

Antenna Placement

Co-Site

Electronics

RF/Antenna and SI/PI/EMI

Antenna Array

Lightening

Strike

© 2011 ANSYS, Inc. April 24, 2015 44


Structural Mechanics

Vibration

Stress/

Explicit Dynamics

Rivet Fatigue

Coupled Solution

Electro-Mechanical

Design

Composites

Failure

© 2011 ANSYS, Inc. April 24, 2015 45

Fluid Dynamics


Landing Deck

Air Flow

Aerodynamics

Engine

Combustion

Landing Gear

Turbulent Flow

Rotor Design and

Aero acoustics

Engine

Cooling

© 2011 ANSYS, Inc. April 24, 2015 46

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

nonlinear effects in active phased array system performanceimapsne.net/2015...

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