Design and Analysis of FSS Radomes
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This document discusses the design and analysis of frequency selective surface (FSS) radomes. It describes various numerical techniques in FEKO software for radome analysis, including the method of moments, finite element method, and multilayer fast multipole method. It also details the radome design process, which involves characterizing individual layers and then analyzing the full radome structure using an impedance sheet approximation to model thin layers. As an example, it characterizes an X-band FSS radome and analyzes its performance at transmitting and rejecting different frequencies.
Design and Analysis of FSS Radomes
- 1. Design and Analysis of FSS Radomes Gopinath Gampala and C. J. Reddy*
- 2. 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 ELECTRICALSIZE COMPLEXITY OF MATERIALS PO/GO UTD
- 3. 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
- 4. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Applications Aircraft Missile Maritime Vehicular Telecom Satcom Air Traffic Control Weather
- 5. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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 ε1ε2 C ε1ε1 ε1ε2 ε2 Dennis J. Kozakoff, Analysis of Radome-Enclosed Antennas, Boston: Artech House, Inc., 1997 Sandwich Design
- 6. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 7. 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 Problems MLFMM ELECTRICALSIZE COMPLEXITY OF MATERIALS PO/GO UTD
- 8. 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
- 9. 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
- 10. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 11. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 12. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 13. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 14. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 15. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 16. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 17. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 18. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 19. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 20. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 21. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 22. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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
- 23. Copyright © 2014 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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