ScienceDirect. Simplified Generation of Electromagnetic Field within EMC Immunity Test Area

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1 Available online at ScienceDiect Pocedia Engineeing 69 ( 014 ) th DAAAM Intenational Symposium on Intelligent Manufactuing and Automation, 013 Simplified Geneation of Electomagnetic Field within EMC Immunity Test Aea Jozef Hallon, Kaol Kováč* Slovak Univesity of Technology in Batislava, Faculty of Electical Engineeing and Infomation Technology, Institute of Electical Engineeing, Ilkovičova 3, Batislava 81 19, Slovakia Abstact Fo electomagnetic adiated immunity testing a homogeneous electomagnetic field within the test aea is equied. Fo this eason floo absobes ae obviously placed between the tansmitting antenna and equipment unde test. The pape analyses the possibility to fulfil homogeneity equiements without the absobes only by changing the antenna height between two positions and by appopiate contolling of test field fequency. The pape demonstates the possibility of this solution with full satisfaction of the field unifomity equiements The The Authos. Authos. Published Published by by Elsevie Elsevie Ltd. Ltd. Open access unde CC BY-NC-ND license. Selection Selection and and pee-eview unde unde esponsibility esponsibility of of DAAAM DAAAM Intenational Intenational Vienna Vienna. Keywods: electomagnetic compatibility; immunity testing; field unifomity 1. Intoduction Accoding to electomagnetic compatibility (EMC) standad equiements thee ae two basic measuements o tests which deal with adiofequency (RF) electomagnetic fields. The fist one is the adiated emission measuement, which is engaged in measuing the field intensity adiated fom the equipment unde test (EUT). Fo this opeation a semianechoic chambe with eflecting floo is pescibed [1]. By this pocedue the eflecting floo simulates the electomagnetic waves eflections fom the eal floo constuction. The second one is the adiated immunity testing. In the fame of this test the homogeneous field is essential fo objectivity and epoducibility of the testing. To maintain the field homogeneity the anechoic o modified semianechoic chambes with RF floo absobes ae equied by standad. The absobes have to be placed between the field souce antenna and EUT []. Changing the floo aangement between both pocedues is cumbesome and equies additional space fo stoage of *Coesponding autho. Tel.: ; fax: addess: kaol.kovac@stuba.sk The Authos. Published by Elsevie Ltd. Open access unde CC BY-NC-ND license. Selection and pee-eview unde esponsibility of DAAAM Intenational Vienna doi: /j.poeng

2 8 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) 7 34 elatively lage absobes. So it would be beneficial to have possibility to pefom the immunity test within the standad test configuation without necessity to use the floo absobes. The test of immunity against electomagnetic field is pat of compulsoy tests against distubing EMC effects. It is pescibed by basic standad EN [1]. This standad ceates the base fo plenty of geneal and poduct specific standads, which ae dedicated to EMC poblem, consequently. The pocedue of immunity testing is two step method. In the fist step test aea of homogeneous EM field, which is named in the standad as unifom field aea (UFA), is calibated in the testing chambe. By calibating pocedue the output levels of signal geneato fo equied fequency points ae obtained. In the second step the immunity test is pefomed using the signal levels collected duing the calibation pocedue. It is evident, that the calibation has to be pefomed elatively aely e.g. once a yea, o if the shielded chambe o the testing equipment is changed. Enfoceability of non-standad test conditions was studied by seveal authos. Thei publications dealt with compaison of test esults obtained in anechoic chambe and in the chambes with diffeent chaacteistics [, 3, 4, 5]. In the pape [6] the authos showed by only expeimental measuements, that it is possible to keep the homogeneity within UFA in equied limits also without the floo absobes by changing the antenna height within the inteval 1 m at 5 points. Thei pocedue needs compute contol system, which pefoms elatively complicated calibation (5 times longe than standad) and it contols the antenna height depending upon the fequency duing the test pocedue. The pesented pape analyses the possibility to ensue the UFA homogeneity by simple way even by maximum two tansmitting antenna heights. Fo this pupose we analyzed the influence of the tansmitting antenna height upon UFA homogeneity at fist by numeical simulation. Consequently we veified the obtained esults by measuement in the semianechoic chambe.. Field homogenity evaluation Fo the calibation of EM field it is necessay to aange a wokplace accoding to Fig. 1. The electic field should be calibated ove a volume o suface in specified distance in font of the adiating antenna. The nom EN specifies the UFA, which is a hypothetical vetical plane of the field in which vaiations ae acceptably small: at each fequency a field is consideed unifom if its magnitude measued at 16 gid points (Fig. 1) is within - 0/ +6 db of the nominal value fo not less than 75 % of all gid points (e.g. if at least 1 of the 16 measued points of an 1.5m 1.5m UFA ae within the toleance) [7]. Moeove the toleance geate than +6 db up to +10 db, but not less than -0 db, is allowed fo a maximum of 3 % of the test fequencies. Fig. 1. (a) Setup of calibation pocedue; (b) Specification of UFA. In the calibation pocedue specified in the standad it is stated that one has to measue the electic field at each one of the 16 gid points of the UFA at the selected fequencies. The fowad powe fom the amplifie to the

3 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) antenna shall be adjusted so that the field stength obtained is equal to the equied calibation field stength E u (electic field calibated in the anechoic chambe). The nom specifies two calibation methods at both vetical and hoizontal polaizations: Constant field stength pocedue, Constant powe pocedue. In the fome pocedue the 16 fowad powe eadings shall be soted into ascending ode and then stating at the highest value one has to check if at least 11 eadings below this value ae within toleance of -6dB/ +0dB of that value. In the latte the 16 field stength eadings shall be soted into ascending ode and then stating at the lowest value one has to check if at least 11 eadings above this value ae within the toleance 0 db/ +6 db of that lowest value. Accoding to this pocedue it is clea that the allowed toleance of + 6 db extendible to + 10 db fo 75 % of all gid points pemits a geat vaiability of the electic field stength unifomity [7]. 3. Analytical desciption of field intensity The situation of the field geneation in any space point of the UFA above eflecting floo is shown in the Fig. on the example of vetical antenna polaisation. Thee ae two adiated waves which paticipate in the field ceation. They ae the diectly popagating wave and the eflected wave. It is evident that the length of wave popagation path is diffeent fo paticula waves. Fig.. Wave paths with the gound plane eflection. The intensity of adiated field fom a dipole with a constant cuent distibution ove the full length can be expessed by the following equations [8]: E E ji L 0 cos j 1 c ji L 0 sin 1 j 1 c 4 0 e 3 jt e j t (1) () The used constants and vaiables ae defined as follows:

4 30 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) distance fom the dipole to obsevation point f - adian fequency c - velocity of light in fee space I 0 - impessed cuent L - length of the dipole = /c - phase constant The electical field at the obsevation point is the sum of the diect and eflected wave multiplied by the eflection coefficient which may be consideed as equal to 1(fo vetical polaization) o -1 (fo hoizontal polaization) as the floo is almost pefectly conducting E E i E (3) The distances fom the dipole to the point of obsevation P can be calculated by equations (4) and (5). Whee h t is the height of the tansmitting antenna and h is the height of the obsevation point P above the gound plane. s is the measuement distance, which is 3 m obviously. The angles i and ae expessed in equations (6) and (7). a a i ht ht h h s (4) ht ht h h s (5) actan h h s (6) i t actan h h s (7) t Thee ae seveal factos influencing the esulting intensity in the obsevation points within UFA. Geneally the intensity of the wave is indiectly popotional to the length of popagation path of the wave i.e. distance between field souce and obsevation point. So the eflected wave has significantly lowe intensity than diect one. Then the phase shift between waves, caused by diffeent popagation path length, significantly affects the esulting field intensity. Both factos, popagation path length and consequently phase shift, ae dependent upon antenna and obsevation point heights. Due to the descibed intefeence of both waves the field intensity is significantly dependent upon fequency and as the popagation distance diffes between UFA points, the field homogeneity is expessively changing up to moe than 0dB at some fequencies. 4. Modelling of testing wokplace To study the EM field intensity distibution in all 16 points of the UFA within the whole fequency ange is athe complicated task. So it would be advantageous to use numeical simulation tool to pefom such study. It allows simple analysis mainly in cases of complicated configuations. Fo this pupose we used softwae system FEKO based on method of moments. The RF absobing walls and ceiling of the test chambe whee modelled by open aea space bode, the conducting floo by pefectly conducting space bode of the model space. Fo simulation of EM field souce we have ceated a model of ou log-peiodic and biconical antennas. The output points of simulation coespond with points of the UFA. An example of simulation esults in gaphical fom is shown in Fig. 3 fo 155 cm antenna height, 45 MHz fequency and 10 V antenna feeding voltage. Thee is the model of log-peiodic antenna visible and the distibution of intensity of EM within the UFA aea. The fluctuation of field intensity caused by intefeence of diect and eflected waves is evident. The intensity is changing fom 3.3 up to 11 V/m, which is moe than 6 db equied by standad. The antenna height was 155 cm, which is geneally equied by the standad, but this height does not suit to ou intention.

5 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) Execution of seaching pocedue It was shown in Fig. 3 that the field intensity can significantly fluctuate within UFA. Although this fact we supposed that the minimum homogeneity fo all antenna heights is lowe than limit value of 6 db. The pinciple of evaluating pocedue was based upon this peposition. So we pefomed homogeneity analyses by numeical simulation in fequency bands MHz and MHz with MHz fequency step. The antenna height was changing in the ange 1.1 m with 10 cm step. Fo each antenna position and each fequency point we stoed the EM field intensity values in all 16 points pescibed by the standad. Then the dependence of UFA homogeneity upon fequency was calculated fo each antenna height and fo both antenna polaization. Fig. 3. Simulated EM field intensity ove a eflective plane at the fequency 45 MHz. Afte collecting of all necessay data the seaching pocedue could stat. It took all combinations of two antenna heights and seached the minimal homogeneity at all fequencies. Then it counts the fequency points fo which the minimal homogeneity is moe then 6 and less than 10 db. If the homogeneity is moe than 10 db, the combination is conside unacceptable. By this pocedue we found out the best combination of antenna heights which wee chosen fo expeimental veification by measuement in semianechoic chambe of ou EMC laboatoy. As the diffeences between the simulation and the measuement esults ae usually not negligible in EMC domain, we pefomed the measuements in some ange aound the chosen antenna heights. Device setup fo calibation pocedue coesponded with Fig. 1. The measuements wee executed by automatic softwae system fully complying the standad equiements fo the UFA calibation and the immunity test pefomance [9], [10]. On the measued data the minimal homogeneity was evaluated by the same pocedue as on the simulation esults. Both the simulation and the measuement esults of the whole pocess ae shown in following diagams. In Fig. 5 the simulated and measued values of homogeneity ae shown fo fequency ange MHz and hoizontal antenna polaization. It is evident fom pesented figues that equied homogeneity is eachable by combination of two antenna heights 130 and 00 cm. This combination allows eaching the best UFA homogeneity, when the 6 db limit value was exceed less than 0.7 db only in 1.73 % of total numbe of fequency values. By veification measuement the 6 db value was exceeded by maximum 0.7 db in 1.96 % of numbe of fequencies. Fo vetical antenna polaization the same analysis was pefomed also. In this case the situation is much bette as the floo eflection coefficient is positive, so the esulting field intensity is not changing so intensively. Ou simulations showed that all heights above 140 cm comply with the equiements of the standad. Duing the measuements all heights above 180 cm wee confoming as is evident on the 190 cm antenna heights example pesented in Fig. 5.

6 3 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) 7 34 Fig. 4. (a) Simulated and (b) measued esults in ange MHz, hoizontal polaization of LP antenna. Fig.5. (a) Simulated and (b) measued esults in ange MHz, vetical polaization of LP antenna.

7 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) The analysis in 1 3 GHz ange was pefomed only by simulation (Fig. 6). Fo hoizontal polaization the homogeneity was confoming by combination of 190 and 00 cm antenna heights, when the limit values 6 db was exceeded by maximum 1. db only fo 1.4 % of fequency points. Fo vetical polaization all heights above 110 cm ae complying. Fig. 6. Simulated esults in ange 1-3 GHz, (a) hoizontal (b) vetical polaization of LP antenna. The esults obtained by numeical simulation and laboatoy measuements in ou semianechoic chambe showed adequate compliance. The esulting diffeences may be due to mild diffeence between ou simulation model and eal semianechoic chambe, which does not have pefectly absobing walls and ceiling as was supposed by the modelling. 6. Conclusion In the pesented pape we found the possibility to fulfil the equiements of the EM field immunity test standad [1] without the floo absobes placed between the tansmitting antenna and the EUT by using only two antenna heights in the fequency ange MHz. This simplifies the wok oganisation in the EMC laboatoy which disposes of only one shielded chambe fo both the adiated field intensity measuements and the field immunity test. By suggested technique it is possible to econfigue the shielded oom fom the configuation of the adiated emission measuement to the configuation of the adiated immunity test pactically by changing the antenna cables fom the measuing eceive input to the powe amplifie output. So the esults of ou wok help to incease the effectiveness of any EMC laboatoy opeation. Because each shielded semianechoic chambe has specific electomagnetic chaacteistics, it is not possible to fully genealize the esults we pesented. Ou chambe has the dimensions of 8.9 x 4.9 x 4.9 m (L x W x H), its walls ae fully coveed by feite absobes and patially by foam absobes fo fequencies above 1 GHz. So it is necessay to appove the poposed pocedue fo each chambe duing its UFA calibation and to obtain the oiginal data sets fo the immunity test by the pocedue we poposed.

8 34 Jozef Hallon and Kaol Kováč / Pocedia Engineeing 69 (014 ) 7 34 Acknowledgements Wok pesented in this pape was suppoted by the Slovak Reseach and Development Agency unde gant No. APVV and by the Slovak Gant Agency VEGA unde gant No. 1/0963/1. Refeences [1] EN :006. Electomagnetic compatibility (EMC). Pat 4-3:Testing and measuement techniques. Radiated, adio-fequency, electomagnetic field immunity test. [] H. Steitwolf, R. Heinich, H.-G. Behnke, L. Dallwitz, U. Kast, Compaison of adiated immunity tests in diffeent EMC test facilities Poceedings, 18th Int. Zuich Symposium on EMC, Munich 007. [3] L. Musso, et al., Radiated Immunity Testing of a Device with an Extenal Wie: Repeatability of Revebeation Chambe Results and Coelation with Anechoic Chambe Results. In: IEEE Int. Symp. on EMC 003, Boston, USA, , p [4] Ch. Tsigos, M. Piette, G. A. E. Vandenbosch, D.V. Toyen, Radiated Immunity in Revebeation and Semianechoic Rooms: Conditions fo Equivalence, IEEE Tans. on Electomagnetic Compatibility, vol. 55, No., 013, pp [5] E. Paez, C. Temola, and M. Azpuua, A poposed method fo quantifying uncetainty in RF immunity testing due to EUT pesence, Pogess In Electomagnetics Reseach B, Vol. 9, 175{190, 011, pp [6] M.J. Windle, S. Ubanski, A Radiated Immunity Unifom Field Ove a Gound Plane. In: IEEE Int. Symp. on EMC 003, Boston, USA, , p [7] B. Audone, I. Maziali, Repeatability and Repoducibility of Radiated Immunity Tests Poc. of the 10th Int. Symposium on Electomagnetic Compatibility (EMC Euope 011), Yok, UK, Septembe 6-30, 011. [8] S. Battemann, H. Gabe, Optimizing an Open Aea Test Site fo Hoizontal and Vetical Polaization, 14th Int. Zuich Symposium on EMC, Zuich 003. [9] J. Hallon, I. Szolik, Test Side Calibation and Contol of Electomagnetic Field Immunity Test. In: Conf. Electical and Powe Engineeing 001, Tenčín, Slovak Republic, , p [10] O. Čičáková, I. Szolik, A. Kamme, Complex System fo EMC Immunity Test. Int. Conf. Applied Electonics 009, Plzeň, 009, p