Document

Report
Project 139: Developing Eco-friendly
Radio Absorbing Materials (RAM) for
Anechoic Chambers
Qian Xu
http://www.cgeinnovation.org/
http://www.rainfordemc.com/
Outline
• Background Information
• Research Questions
• Systematic Solutions
Qian Xu, 2
Background Information
Micro-level
Macro-level
How to design
the chamber
?
Pictures from: ETS LINDGREN
http://www.ets-lindgren.com/
Pictures from: www.cst-china.cn
Qian Xu, 3
William H. Emerson, IEEE Trans. on Antenn. And Propag., Vol. AP21, No. 4, July, 1973.
• Mid 1930’s: Theoretical and experimental work.
• 1936: First patented absorber.
• WWII(1939-1945): Germany: Schornsteinfeger(Wesch
material & Jauman absorber ), US: HARP(Halpernanti-radar-paint) by Halpern at MIT Radiation
Laboratory, Salisbury screen.
• 1945-1950: 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.
Qian Xu, 4
S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi, PIER B,
Vol. 19, 367-383, 2010.
Qian Xu, 5
Outline
• Background Information
• Research Questions
• Systematic Solutions
Qian Xu, 6
Research Questions
1. How to choose/analyse/optimise RAM?
Ferrite tiles
Hybrid
Pyramid
Pictures from: http://www.rainfordemc.com/anechoic-materials.html
Qian Xu, 7
Research Questions
2. How to design/analyse/optimise the whole chamber?
Tapered Chamber
Picture from:
http://www.mobilemag.com/2010/07/16/apples100-million-test-chamber-droid-eris-andblackberry-bold-9700-suffer-the-same/
Compact Chamber
Aircraft Chamber
Picture from:
http://gtresearchnews.gatech.edu/gtricompact-range/
Picture from:
http://www.rainfordemc.com/aircraftchamber.html
Qian Xu, 8
Outline
• Background Information
• Research Questions
• Systematic Solutions
Qian Xu, 9
Systematic Solutions: Macro-level
• Key problem: Whole chamber design
Trial and error/cut and try
Ray Tracing
Full wave simulation
Accuracy
• Commercial Software: CST (FEM, FITD), HFSS (FEM),
Feko (MoM)
• Friendly GUI, General simulation software, Pricy, High
performance computers(cluster), Time consuming
Qian Xu, 10
Trial and error
• Empirically based, mostly determined by lower frequency limit.
• Thickness~Reflectivity
W=1/2L
• Extraneous energy level~Reflectivity (Free Space VSWR
Method)
Picture from: Electromagnetic Anechoic Chambers A Fundamental Design
and Specification Guide, Leland H. Hemming, Chapter 9.3.2
Qian Xu, 11
Free Space VSWR Method
Repeated again for horizontal and vertical polarisation.
Qian Xu, 12
Free Space VSWR Method
Ripple:
Extraneous
signal :
If a 0.3dB ripple
is observed 20dB
down from the
peak, the
extraneous signal
level is -55dB
Qian Xu, 13
Full Wave Method
• Algorithm limit
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
• Consider lossy(inhomogeneous) material
FEM, FDTD, GO
Qian Xu, 14
Ray Tracing/GO(Geometric Optics)
• High frequency approximation
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
Qian Xu, 15
Ray Tracing/GO Workflow
Modified rectangular, Compact Range, Tapered
Preprocessing: Modeling (.stl)
Mesh Generation,
Material/Boundary Assignment
GND, side-wall, back-wall….
different area with different reflectivity
Ray Tracing Code
GPU,
Parallel
Field Distribution
1st order, 2nd order, 3rd order reflection
(Propagation direction, Amplitude, Phase)
Performance & Cost
Qian Xu, 16
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, 367387, 2010.
Qian Xu, 17
Thank you!

similar documents