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**Project 139: Developing Eco-friendly Radio Absorbing Materials (RAM) for Anechoic Chambers**

Qian Xu

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Outline Background Information Research Questions Systematic Solutions

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**Background Information**

Micro-level Macro-level RAM Type? RAM Thickness? How to design the chamber ? Field Uniformity? Chamber Shape? RAM Arrangement? Pictures from: ETS LINDGREN Pictures from:

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**William H. Emerson, IEEE Trans. on Antenn. And Propag., Vol. AP-21, No. 4, July, 1973.**

Mid 1930’s: Theoretical and experimental work. 1936: First patented absorber. WWII( ): Germany: Schornsteinfeger(Wesch material & Jauman absorber ), US: HARP(Halpern-anti-radar-paint) by Halpern at MIT Radiation Laboratory, Salisbury screen. : Broad-band absorber. The early 1950’s: First “dark rooms”. The late 1950’s: New generation of broad-band. absorbers(-40dB normal), antenna pattern comparison method, new chamber shape, shielded anechoic chambers. 1960’s: Low frequency absorber(-40dB 100MHz), 3rd generation RAM (-60dB normal), improved absorber measurement(Free-space VSWR), tapered chamber by Emerson.

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**S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi, PIER B, Vol**

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Outline Background Information Research Questions Systematic Solutions

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**Research Questions 1. How to choose/analyse/optimise RAM?**

Ferrite tiles Hybrid Pyramid Pictures from:

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Research Questions 2. How to design/analyse/optimise the whole chamber? Tapered Chamber Compact Chamber Aircraft Chamber Picture from: Picture from: Picture from:

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Outline Background Information Research Questions Systematic Solutions

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**Systematic Solutions: Macro-level**

Key problem: Whole chamber design Commercial Software: CST (FEM, FITD), HFSS (FEM), Feko (MoM) Friendly GUI, General simulation software, Pricy, High performance computers(cluster), Time consuming Trial and error/cut and try Ray Tracing Full wave simulation Accuracy

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Trial and error Empirically based, mostly determined by lower frequency limit. Thickness~Reflectivity Extraneous energy level~Reflectivity (Free Space VSWR Method) W=1/2L Picture from: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 9.3.2

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Free Space VSWR Method Repeated again for horizontal and vertical polarisation.

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**Free Space VSWR Method If a 0.3dB ripple**

Extraneous signal : If a 0.3dB ripple is observed 20dB down from the peak, the extraneous signal level is -55dB

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**Full Wave Method Algorithm limit**

Consider lossy(inhomogeneous) material FEM, FDTD, GO N PO/SBR/GO N*log(N) MLFMM N1.1~1.2 FDTD N2 FEM N3 MoM Frequency Electrical Size /Physical Size Electrical Volume 10MHz 0.5λ/15m 0.125λ3 100MHz 5λ/15m 125λ3 1GHz 50λ/15m 125E3λ3 10GHz 500λ/15m 125E6λ3 40GHz 2000λ/15m 8E9λ3

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**Ray Tracing/GO(Geometric Optics)**

High frequency approximation 2nd order 1st order T=R+G+P(dB) normalized to direct ray in dB Ref: Electromagnetic Wave Theory, J. A. Kong, p.722. T=Total strength R=reflection coefficient G=Antenna pattern gain P=Propagation parameter Ref: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 5.2.3

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**Ray Tracing/GO Workflow**

Preprocessing: Modeling (.stl) Modified rectangular, Compact Range, Tapered Mesh Generation, Material/Boundary Assignment GND, side-wall, back-wall…. different area with different reflectivity Ray Tracing Code Field Distribution 1st order, 2nd order, 3rd order reflection (Propagation direction, Amplitude, Phase) GPU, Parallel Performance & Cost

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**Expected Results Performance Field uniformity (±?dB) Cost**

Debug/Optimize 1st order, 2nd order, 3rd order reflection can be used to find the source of extraneous signal. Ref: Minimum usage of ferrite tiles in anechoic chambers, S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi. PIER B, Vol. 19, , 2010.

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Thank you!

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MULT. INTEGERS 1. IF THE SIGNS ARE THE SAME THE ANSWER IS POSITIVE 2. IF THE SIGNS ARE DIFFERENT THE ANSWER IS NEGATIVE.

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