design and analysis of fss radomes
TRANSCRIPT
Design and Analysis of FSS Radomes
Gopinath Gampala and C. J. Reddy*
Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Outline
• Introduction
• Radome Analysis Methods
• Radome Design Process
• Characterizing FSS Radome Layered Configuration
• Impedance Sheet Approximation
• Conclusion
FDTD
FEM
MOM
Hybridisation to
solve large and
complex problems
MLFMM
EL
EC
TR
ICA
L S
IZE
COMPLEXITY OF MATERIALS
PO/GO
UTD
Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Radome
• Radome (Radar Dome) is a Structural, Weatherproof Enclosure that
Protects an Antenna/Radar System
• Radome Should Minimally Attenuate the Electromagnetic
Signal Transmitted or Received by Antenna/Radar System
• Radomes Can be Constructed in Several Shapes
Depending on the APPLICATION
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Applications
Aircraft
Missile
Maritime
Vehicular
Telecom
SatcomAir Traffic Control
Weather
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Radome Wall Types
• Radomes can be Classified into Monolithic and Sandwich Designs,
based on Wall Construction
Monolithic
A-Sandwich: ε1 > ε2
B-Sandwich: ε1 < ε2
C-Sandwich: ε1 > ε2
A or B
ε1 ε1 ε2
C
ε1 ε1 ε1 ε2 ε2
Dennis J. Kozakoff, Analysis of Radome-Enclosed Antennas,
Boston: Artech House, Inc., 1997
Sandwich Design
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Radome-Induced Effects
• Radome Changes the Electrical Performance of Antenna Because of
Following Factors:
— Dissipative Losses Within a Dielectric Material
— Electrical Phase Shifts Introduced by Presence of Radome
— Internal Reflections
• The Changes (above) Produced by Radome Manifest Themselves
into Radome Performance Parameters
— Radome Insertion Loss (Radome Loss)
— Increased Antenna Sidelobe Levels
— Boresight Error (BSE)
Dennis J. Kozakoff, Analysis of Radome-Enclosed Antennas,
Boston: Artech House, Inc., 1997
Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
FDTD
CEM Methods in FEKO
Methods for
Geometrically
Complex
Problems
FEM
MOM
Hybridisation to
solve large and
complex
problems
Methods for
Electrically
Large
ProblemsMLFMM
EL
EC
TR
ICA
L S
IZE
COMPLEXITY OF MATERIALS
PO/GO
UTD
Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Radome Analysis Techniques
• FEKO Offers Several Numerical Methods to Analyze the Radomes
for Radome-Induced Effects
— MoM and FEM for Electrically Small Radomes
— MLFMM and RL-GO for Electrically Large Radomes
— TDS Approximation for Thin Walled Radomes
• TDS can be used in combination with MoM, MLFMM
and RL-GO
MoM : Method of Moments
FEM : Finite Element Method
TDS : Thin Dielectric Sheet
MLFMM : Multi-Level Fast Multipole Method
RL-GO : Ray-Launching Geometrical Optics
Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Specialty Radomes
• There is More to the Types of Radomes than Just Dielectric-Layered
Wall Radomes
— Frequency Selective Surface (FSS) Radome is One Such Specialty
Radome
• FSS Radome Includes a Curved FSS within a
Multilayered Dielectric Wall Radome
— FSSs are Periodic Surfaces in Two Dimensions
— FSSs Have Inherent Filtering Characteristics
• FSS Radomes are Useful to Reduce RCS Over a
Wide Frequency Range Due to Bandpass/Bandstop
Characteristics
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Radome Design Process
• The First Step in Designing a Radome Would be the
Order and Choice of Radome Wall Layer Materials
— The Radome Wall Materials Can be characterized
Through the Transmission Loss Analysis
• Next Step in the Design Process Would be Building
the Complete Radome and Analyze for Radome
Induced Effects
— Wall Layer Configuration with Optimal Transmission
Performance is Used to Build the Complete Radome
— Radome Induced Effects are Computed with the
Radome Protecting the Antenna it is Built for
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Radome Wall Material Characterization
• FEKO Offers Two Fast and Accurate Methods to Calculate the
Transmission Loss Through the Radome Layers
Planar Green’s Functions Periodic Boundary Conditions
– Planar Green’s Functions
• No Unknowns
• Highly Efficient i.t.o. Both Time and Memory
– Periodic Boundary Conditions
• Infinite Layers Realized with Single Small Unit Cell
• Huge Reduction in No. of Unknowns
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Special (Planar) Green’s Function Example
• Consider an A-Sandwich Radome (Style-c)
• Layer Configuration
Quartz Polycyanate Skins
εr = 3.23
tan δ = 0.016
h = 0.0762 cm
Phenolic Honeycomb Core
εr = 1.10
tan δ = 0.001
h = 1.0160 cm
Dennis J. Kozakoff, Analysis of Radome-Enclosed Antennas,
Boston: Artech House, Inc., 1997
Radome Layers Designed using Planar
Green’s Functions
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FEKO vs Literature
Transmission Loss at Different
Incidence Angles
FEKO Agrees Very Well With
Published Results
Dennis J. Kozakoff, Analysis of Radome-Enclosed Antennas,
Boston: Artech House, Inc., 1997
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SGF vs PBC
• Consider a Monolithic Thin-Walled Radome
• Layer Configuration
Dielectric Constant = 4
Loss Tangent = 0.015
Dennis J. Kozakoff, Analysis of Radome-Enclosed Antennas,
Boston: Artech House, Inc., 1997
Radome Layer Designed using
PBC
Radome Layer Designed using
SGF
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SGF vs PBC
Both the Methods Agree with Each Other
SGF – Special (Planar) Green’s Functions
PBC – Periodic Boundary Conditions
Wall Thickness = 0.1 λ Wall Thickness = 0.2 λ
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X-Band FSS Radome Characterization
• A-Sandwich Radome FSS Radome
—Jerusalem Cross FSS Layer in the Middle of the Core of A-Sandwich
Configuration
• A-Sandwich Layer Configuration
— 0. 319 mm Thick Quartz Polycyanate Skins
• εr = 4.8, tan δ = 0.0002
— 1.595 mm Thick Phenolic Honeycomb Core
• εr = 1.3, tan δ = 0.001
• FSS Layered Configuration Can be Characterized Through Transmission
Loss Analysis
— PBC is the Best Approach to Characterize FSS Layered Configuration
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Pass Band FSS Radome
• The FSS Radome Was Designed for X-Band (9.4 GHz) Radar Applications
— The A-Sandwich FSS Configuration Has a Passband Centered at 9.4 GHz
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Full Radome Analysis
• Next in Design Process is Building a Full 3D Model of the Radome to
Analyze for Radome Induced Effects
• A Radome with All Explicit Layers is a Computational Nightmare
— The Analysis is Near-impossible if the Layers are Electrically Too Thin
• TDS Approach Won’t Account for the FSS Layer
• FEKO Offer an Impedance Sheet Approximation Solution
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Impedance Sheet Approximation
• FEKO Offers the Ability to Define a Frequency-Dependent Impedance
Sheet
— LUA Scripting is Integrated into FEKO
— Use the Script to Convert Transmission/Reflection Coefficients into
Impedance Parameters
— Use the Impedance Parameters to Define an Impedance Sheet in Place of
Explicit Radome Layers
• Huge Reduction in Number of Unknowns → Tremendous Savings in
Computational Resources
LUA Script
Τ, Γ → Z
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Explicit Layers vs. Impedance Sheet
• The Impedance Sheet Approximation is as Accurate as Modelling Explicit Layers
• Computational Resources:
— Explicit Layers: 1.7 GB of Memory and 14.5 hours Run-time
— Impedance Sheet: 2.4 MB of Memory and 0.1 hours Run-time
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Radome Induced Effects at 9.4 GHz
• A Nosecone Shaped Radome
Protecting the Vivaldi Antenna
— The Full 3D Radome is Built Using the
Impedance Sheet Approximation
• As Intended, the Radome is
Completely Transparent to the RF
Signal at the Center of Pass Band
• The Sidelobe Levels are Unaffected
• Negligible Boresight Error
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Radome Induced Effects at 12.5 GHz
• At 12.5 GHz (Outside the Passband),
the Radome Rejects Most of the
Radiation
• This Characteristic is Extremely Useful
in Reducing the Out-of-Band RCS
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Conclusion
• FEKO Offers Various Solvers for the Design and Analysis of
Radomes
• Periodic Boundary Conditions are Extremely Useful in Characterizing
a Layered FSS Radome Configuration
• The Impedance Sheet Approximation is an Efficient and Accurate
Solution to an Otherwise Complex Thin-Walled FSS Radome
Analysis