3 Background Information Micro-level Macro-levelRAM Type?RAM Thickness?How to design the chamber?Field Uniformity?Chamber Shape?RAM Arrangement?Pictures from: ETS LINDGRENPictures from:
4 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.
5 S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi, PIER B, Vol
10 Systematic Solutions: Macro-level Key problem: Whole chamber designCommercial Software: CST (FEM, FITD), HFSS (FEM), Feko (MoM)Friendly GUI, General simulation software, Pricy, High performance computers(cluster), Time consumingTrial and error/cut and tryRay TracingFull wave simulationAccuracy
11 Trial and errorEmpirically based, mostly determined by lower frequency limit.Thickness~ReflectivityExtraneous energy level~Reflectivity (Free Space VSWR Method)W=1/2LPicture from: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 9.3.2
12 Free Space VSWR MethodRepeated again for horizontal and vertical polarisation.
13 Free Space VSWR Method If a 0.3dB ripple Extraneous signal :If a 0.3dB rippleis observed 20dB down from the peak, the extraneous signal level is -55dB
15 Ray Tracing/GO(Geometric Optics) High frequency approximation2nd order1st orderT=R+G+P(dB)normalized to direct ray in dBRef: Electromagnetic Wave Theory, J. A. Kong, p.722.T=Total strength R=reflection coefficientG=Antenna pattern gain P=Propagation parameterRef: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 5.2.3
16 Ray Tracing/GO Workflow Preprocessing: Modeling (.stl)Modified rectangular, Compact Range, TaperedMesh Generation,Material/Boundary AssignmentGND, side-wall, back-wall….different area with different reflectivityRay Tracing CodeField Distribution1st order, 2nd order, 3rd order reflection(Propagation direction, Amplitude, Phase)GPU,ParallelPerformance & Cost
17 Expected Results Performance Field uniformity (±?dB) Cost Debug/Optimize1st 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.