Proceedings CEEM'2009/Xi'an

Research on the Substitute Method of Electromagnetic Emulation

for Reverberation Chamber

Pan Xiaodong', Wang Qingguo', Dai Hongbin2, FAN Li-si'

( 1. Electrostatic and Electromagnetic Protection Research Institute, Mechanical Engineering College,Shijiazhuang,050003,China

2. Department ofBasic Courses, Mechanical Engineering College, Shijiazhuang 050003, China)

Abstract: Finite array of continuous wavesuperposition was adopted to simulateelectromagnetic environment of reverberationchamber. Using this equivalent method it isnot necessary to divide cavity mesh grid andcalculate the reflect process of the chambercavity time after time. So it becomes possiblefor electric large scale reverberation chamberto carry out high frequency electromagneticemulation.

Key words: reverberation chamber,electromagnetic emulation, continuous wave,random matrix, FEKO

With the establishment and compulsoryexecution of domestic and internationalelectromagnetic compatibility (EMC)criterion/instruction and standard, the EMCof electronic equipment has been concernedincreasingly. As a new kind of EMC test site,the reverberation chamber (RC) can producehigher electric field with lower power input,thus it has been extensively concentrated onby people since its coming out. Further more,it has become the current hot spot problem ofEMC research domain [1].

At present, the domestic andinternational research on RC is mostlyconcentrated on optimization of structuredesign, electromagnetic test, effectexperiment and so on. As for the aspect ofelectromagnetic emulation research, becauseof dividing a mass of mesh grid for RC cavityand calculating the establishment ofcompound field reflected by the RC cavity,the computation quantity of emulation is toolarge and the high frequency emulation of

electric large scale RC is limited. Now it isurgent to explore the substitute method ofelectromagnetic emulation for RC.

1 The principle of substitute method forelectromagnetic emulation

Generally speaking, when it comes toelectromagnetic emulation for RC, firstly thecavity, emission antenna, EUT andcalculation space are required to divide meshgrid and establish mesh model. Secondly theexcitation source is added on emissionantenna, the boundary condition andcomputation parameter are set. Lastly theemulation can be carried out. Under thecondition of certain computer hardwareperformance, the computation time ofemulation is decided on the quantity of meshgrid, and the precise of emulation is decidedon the nicety level (generally the dimensionof mesh grid is much smaller than thewavelength). So in order to ensure the preciseof emulation, the quantity of mesh grid is toolarge especially for high frequency and largescale structure, even it is impossible to finishthe emulation under the condition of exitingcomputer performance. In order to solve theproblem, the substitute method ofelectromagnetic emulation is taken intoaccount. Under the precondition ofunchangeable nicety level for mesh model,the substitute method reduces mesh gridquantity to raise calculation efficiency.

According to principle of work for RC,the electromagnetic energy transmits to RCby the way of radiation through emissionantenna. The electromagnetic energy is

The project supported by national natural science foundation of China.Code: 60671045,50877079

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reflected by the wall, the roof, the floor andthe stir, so the electromagnetic field in RCtest space is superposed by reflectingelectromagnetic wave. Because the stirchanges the boundary condition ofelectromagnetic field in RC, the transmissiondirection, phase, polarization of reflectingelectromagnetic wave which reaches to acertain test point in RC obey probabilityuniformity distribution, so theelectromagnetic field has the characteristic ofstatistic uniformity, random polarization andisotropy [2]. In view of above-mentionedtheory, finite array of continuous wavesuperposition generated by computer wasadopted to simulate electromagneticenvironment in RC. The transmissiondirection, polarization and phase angle of thecontinuous wave vary randomly. This kind ofequivalent simulation method need notestablish the mesh grid model of RC cavityand greatly reduces the mesh grid quantity. Atthe same time, the compound electromagneticfield environment can be established withoutcalculating the reflect process time after timeof the chamber cavity. Thus the quantity ofcalculation is reduced greatly and it makesthe high frequency electromagnetic emulationin RC became possible [3,4].

The parameter (), ffJ , 1J, 5 are set torepresent pitching angle, azimuth angle,polarization angle and phase angle of theincidence continuous wave separately. Theparameter n is set to represent the number ofcontinuous wave. To ensure the fieldsuperposed by finite array of continuouswave has the typical characteristic ofcompound field in RC (statistic uniformity,random polarization, isotropy), the method ofproducing random matrix by computer isadopted to generate n array of continuouswave with random pitching angle, azimuthangle, polarization angle and phase angle. Sothe n array of complete random continuouswave can be superposed to simulate thecompound electromagnetic field in RC.

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2 Realization of emulation process

In order to realize the principle above,the software MATLAB call the kernelprogram RUNFEKO in the electromagneticemulation software FEKO to carry outemulation analysis. MATLAB modify *.prefile produced by EDITFEKO in loopstatement program, which makes that theexcitation source is superposed by n array ofrandom continuous wave. RUNFEKO call thenew generating file *.pre to carry out theemulation. The program POSTFEKO uses tocarry out post process.

2.1 Superposition of n array of randomcontinuous wave

The random matrix of n X 4 is producedby computer. The 4 column represent pitchingangle, azimuth angle, polarization angle andphase angle separately. At the same time, therandom number in the matrix is fit for itsvalue range. So the continuous wave can bedetermined by every row data in matrix.Therefore, the superposition of n array ofcomplete random continuous wave can be getthrough inputting n row data in matrix toFEKO.

Due to adopting sphere coordinatesystem to add excitation source in FEKO, ifcomputer generates random number directlyin sphere coordinate system, it is not randomdistribution according to the sphere face for narray of continuous wave. The distributiondensity of continuous wave in the two polesis larger than in the equator. Therefore dotransformation as follows: Computergenerates random matrix A of m X 3 (thevalue of matrix A changes from -0.5 to 0.5).The row vector of matrix A represent thepoint coordinates in Cartesian coordinate. Somatrix A represent m points randomdistributing in cube (the length of cubic is 1,the central point of cube is located in originof coordinate). The section of cube is shownin Fig.I. The random points which conform

Proceedings CEEM'2009/Xi'an

to the equation x 2 + y2 + Z2 ::;; 0.52 arewritten in matrix B. if there are n pointsconforming to the equation above, the matrixB (n X 3) represents n points randomdistributing in sphere with radium 0.5. Thexoy section of sphere is shown in Fig.2. Therandom points in shadow are the availablepoints. The rectangular coordinates in matrixB are transformed to sphere coordinates toproduce pitching angle and azimuth angle forn array of random continuous wave.Furthermore, the computer producepolarization angle and phase angle changingfrom 0 to 2 n random for n array of randomcontinuous wave. At last, the n group ofrandom B, rp, 1]' 8 are input to FEKO toproduce n array of continuous wavedistributing in sphere random. It is shown inFig.3.

sections, it is shown in FigA, the E-fielddistribution under the condition of 1000 arrayof random continuous wave superpositionwas calculated. The results of E-fielddistribution at a certain time are shown inFig.5.

Fig.4 The orthogonal section tor calculation

FIg.! The xoy section of cube Fig.2 The xoy section of sphere

Fig.3 Random distributing continuous wave

Fig.5 E-field oforthogonal section at sometime

The color in the figure represents thestrength of the E-field. The distribution of theE-field is relative homogeneous. There is noobvious discrepancy on the three orthogonalsections. Eight points were picked randomly.The maximum E-field in x, y, z directionwere obtained separately [5]. It is shown inTab.I. The unit ofE-field is Vim.

2.2 The E-field distribution of randomcontinuous wave superposition

When the frequency of the excitationsource is IGHz, on the three orthogonal

• • • •• • • • • •• • • •

~ • • • • •• • • • •

• • • .

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Proceedings CEEM'2009/Xi'an

Tab.2 The statistic analysis result of 8 random points

3 Conclusions

(Ex) 8 (E y) 8 (E z) 8 (E) 24 Ox Oy Oz 024

19.37 18.11 19.10 18.86 2.57 2.36 2.45 2.38

x 27.46 13.69 9.47 24.88 17.17 13.75 25.14 23.36

Y 10.14 18.43 17.48 29.47 13.67 20.80 18.45 16.42

z 22.22 11.96 5.16 11.62 30.08 21.04 18.08 22.64

[lJ Zhang Chenghuai. Research on Test Method of theElectromagnetic Environment Effect and TheirCorrelation in Reverberation Chamber and GTEMCell[DJ. Shijiazhuang, Ordnance EngineeringCollege, 2008.

[2J J. G. Kostats, B. Boverie. Statistical model fora mode-stirred chamber [JJ. IEEE Transactions onElectromagnetic Compatibili~y, 1991, 33(4):366 - 370.

[3J HILL 0 A. Plane wave integral representation forfields in reverberation chambers[JJ. IEEETransactions on Electromagnetic Compatibility,1998, 40(3) :209-217.

[4J Franco Moglie, Anna Pia Pastore. FDTD Analysis ofPlane Wave Superposition to SimulateSusceptibility Tests in Reverberation Chambers[JJ. IEEE Transactions on ElectromagneticCompatibility, 2006, 48(1) :195-202.

[5J Q. G. Wang, E. W. Cheng. Optimization ofcalibration procedure for reverberation chamberbased on NI LabVIEW platform[CJ. Qingdao: 20074th International Symposium on ElectromagneticCompatibility Proceeding, 2007.

Reference:

Consequently, the field uniformity should beinspected when using this substitute methodto carry out emulation. If the field uniformitycan't conform to the requirement of thestandard, the new random characteristic valueof the incidence continuous wave should begenerated, and then to carry out the emulationonce more.

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Tab.l The maximum E-field of8 random points

Through statistical analysis, the averagevalue and standard deviation of the E-fielddistribution show as Tab.2. The unit ofE-field and the standard deviation is V1m anddB separately. It can be seen from the tablethat the standard deviation of x, y, z directionare all smaller than 3dB, which conform tothe requirement of uniformity in the standard"BS-EN61000-4-21 the test method ofreverberation chamber". Therefore, adoptingthis equivalent substitute method to simulatecompound field environment in RC isfeasible. On this foundation, other effectexperiment emulation also can be carried out.

This paper provides a kind of equivalentsubstitute emulation method for RC. Finitearray of continuous wave superposition wasadopted to simulate electromagneticenvironment in RC. Using this equivalentmethod it is not necessary to divide cavitymesh grid and calculate the reflect process ofthe chamber cavity time after time. So itbecomes possible for electric large scalereverberation chamber to carry out highfrequency electromagnetic emulation.

Because the characteristic parameters ofthe fmite array of continuous wave aregenerated by computer randomly according toits value range, so the little probability thatthe field uniformity isn't conform to thestandard requirement may happen.

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