Application of TEM horn antenna in radiating NEMP simulator

Transcription

1 Journal of Physis: Conferene Series Appliation of TEM horn antenna in radiating NEMP simulator To ite this artile: Yun Wang et al 013 J. Phys.: Conf. Ser View the artile online for updates and enhanements. This ontent was downloaded from IP address on 1/10/018 at 17:10

2 7th International Conferene on Applied Eletrostatis (ICAES-01) Journal of Physis: Conferene Series 418 (013) 010 Appliation of TEM horn antenna in radiating NEMP simulator Yun Wang 1, Yongguang Chen, Qingguo Wang 1. Department of Postgraduate, the Aademy of Equipment, Beijing , China;. Institute of Eletrostati and Eletromagneti Protetion, Mehanial Engineering College, Shijiazhuang, , China Abstrat. In order to design a small radiating nulear eletromagneti pulse simulator with fast rise time, we have investigated the appliation of TEM horn antenna in this kind of simulator. The TEM horn antenna is exitated by the integral double exponential pulse. Farfield response in time domain is analyzed based on the step response formula whih is derived from the equivalent transmission line model of TEM horn antenna. Priniple of antenna parameters seletion is determined. The results of numerial alulation give a show of the radiation waveform and some problems. Then experiments are implemented and results are ompared with the radiation waveforms generated by double exponential pulse exitation. It suggests that the TEM horn antenna an be used as radiating antenna in the NEMP simulator, whih an radiate double-exponent-like pulse with the integral double exponential pulse as exitation. Meanwhile, impedane loading an improve farfield waveforms and enhane the low-frequeny radiating ability of antenna. 1. Introdution Nulear eletromagneti pulse simulators (NEMPS) are usually used to produe nulear eletromagneti pulse (NEMP) environment by generating double exponential pulse approximately when testing NEMP s eletromagneti effet. At present, international and domesti waveform standards have been made for eletromagneti pulse (EMP) simulators. In 1999, the U.S. standard MIL-STD-461E [1]. speified following standards: EMP waveform peak value is 50 kv m -1, rise time is ns, and half peak pulse width is 3±5 ns. Our ountry has released similar waveform standard GJB1389A-005 []. All these standards have shorter rise time and narrower pulse width than old standards (suh as the 1986 U.S. standard MIL-STD-461C [3], 1993 U.S. standard MIL-STD-461D [4] et.). Rise time of pulse generated by traditional NEMPS (suh as bounded wave simulator, stati simulator, et. [5]) is not fast enough beause of the transmission line struture. However, the radiating EMP simulators using antenna struture an get faster rise time and larger test spae without speial requirements, whih benefit to the EMP effet experiments for large equipment. Nowadays age-like dipole antennas are ommonly used [6] with the features of onstant impedane, broad band and good field uniformity parallel to the axis. However, the volume of this kind of antenna is generally very huge, rise time is longer, diretionality is poor, and the effetive test area is small. In this paper, TEM horn antenna is tried for NEMPS, whih has been widely adopted in ultra wideband fields [7] as a pulse radiating antenna with a ertain diretivity, wide bandwidth and To whom any orrespondene should be addressed. Published under liene by Ltd 1

3 7th International Conferene on Applied Eletrostatis (ICAES-01) Journal of Physis: Conferene Series 418 (013) 010 the phase entre of radiation invariane. Theoreti analysis and numerial simulation as well as experiment are implemented. Results show that TEM horn antenna an be used as the radiating antenna in EMP simulator if its low frequeny radiation performane an be improved.. Basi theory of TEM horn antenna As shown in figure 1, TEM horn antenna is omposed of two triangular metalli plates. The intersetion angle is β. Eah plate s flare angle isα. Antenna length is expressed by l, height by h, width by w. The harateristi impedane of antenna is Z. For TEM horn antenna with small flare angle, urrent distribution on plates is mainly omposed of the longitudinal omponent along with Z diretion. Therefore, in literature [8], TEM horn antenna an be desribed by a transmission line iruit model with terminal open. Based on this equivalent model, a formula of step response for radiation on the antenna s axis is given: ( l 0 1 t TOT V l ) t r r tr E% l y (, r tr) = Ey e u( tr) [(1 e )( u tr) (1 e )( u tr )] rh lω r+ l where ut () is the step pulse; tr = t ; is light veloity; r is the far-field distane shift from the antenna aperture; = π f,whih means high frequeny ut-off point in antenna frequeny response; small flare angle, w V0 is the input voltage peak, Ey = Ea ( V0 / h) ; for TEM horn antenna with Ey 1. From the frequeny response asymptotes of the TEM horn with step exitation shown in figure 7 of literature [8], we get that: f f 1 = () πl lf E = (3) h g y This frequeny response an be viewed as the band pass filter. In the pass band, the urve is smoothing, whih means that radiation waveforms keep up with the differential form of pulse exitation. So in order to get double-exponent-like pulse radiation field, we need to use the integral double exponential pulse exitation. (1) Figure 1. Diagram of the TEM horn antenna.

4 7th International Conferene on Applied Eletrostatis (ICAES-01) Journal of Physis: Conferene Series 418 (013) Farfield in time domain with integral double exponent pulse exitation. The atual systemi response is the onvolution of step response and the differential form of atual input voltage. Using formula (1), the formula of radiation farfield response in time domain an be dedued for TEM horn antenna exitated by arbitrary pulse: TOT dv () t E% y ( r, t) = formula(1) dt 0 tr < 0 V0 l 1 V0 l 1 l = Ey A [ B C] = Ey A1( tr) B1( tr) 0 tr < r h l ω r h l ω V0 l 1 l l Ey A1( tr) [ B1( tr) B1( tr )] tr > r h l ω Where dv () t = V1 () t u() t indiates that V () t 1 only has meaning at t 0, and dt t A = e r u tr V1 t u t = A1 tr u t r ( ) () () ( ) ( ); B= e ut V tut = B t ut t t A1() t = e u() t V1() t u() t B1( t) = (1 e ) u( t) V1( t) u( t) l ( tr ) l l C = (1 e ) u( tr ) V1( t) u( t) = B1( tr ) u( t l r ) Aording to IEC [1], we an get the integral double exponential pulse, Here =50 kv m E 0 0 t 0 V () t = E 0 τt τ1t k ( τ1e τ e ) t > 0 ττ 1 τ1 τ (4) t (1 r ) ( r) 1( ) ( ) 1( r) ( r); -1, = s -1, = s -1, k =1.3, pulse duration time T =100 ns. (5) Figure. Radiated waveforms for different antenna length. 3

5 7th International Conferene on Applied Eletrostatis (ICAES-01) Journal of Physis: Conferene Series 418 (013) 010 Figure 3. Comparison of farfield waveforms. Set the antenna length as 1.6 m, 7 m, 16 m, respetively, the orresponding antenna height are 1.55 m, 3.4 m, 4.90 m, using integral double exponential pulse exitation, the far field radiation waveforms on the antenna s axis are shown in figure, whih indiate that the amplitude of radiation field beomes large, the pulse width is broadening, and the pulse form is gradually lose to double exponential pulse with the antenna length and height inreasing. However, the zero-rossing phenomenon beomes serious, the negative peak value is larger and the waveform after zero omes to be poor. 4. Simulations and experiments Now we exeute some simulations and experiments to have a farther analysis for the TEM horn antenna Priniple of antenna parameters seletion There are 5 parameters whih are l h w α and β. Aording to the geometri features, the relationship between them is shown as follows: h β = atan l w β α = atan sin h w In this formula, the ratio of is determined.by harateristi impedane Z, whih an be h alulated by the formula (1) and () in literature [9]. Aording to the above analysis, the priniple of TEM horn antenna parameters seletion an be summarized as: with Z known, is generally taken as one, we need firstly to determine the E y antenna length l and height h aording to frequeny range f ~ 1 f by formula () and (3); and then get the values of aperture width w and struture angle ( α, β ) by the formulas in literature [10]. (6) 4

6 7th International Conferene on Applied Eletrostatis (ICAES-01) Journal of Physis: Conferene Series 418 (013) Numerial modeling and simulation results Aording to the above priniple, let f 1 = 3 MHz, f = 400 MHz, Z = Z0 = 377Ω, then we an get that: l 16 m, h 4.89 m, w 0.85 m, α 3 o o, β 17. With integral double exponential pulse as exitation, based on the finite integral in time domain (FITD) method [11], the farfield waveform of 50 m away from the antenna aperture, ompared with the theoretial value (beause of the differene between antenna and equivalent transmission line model, the farfield amplitudes are not omparable, so both the simulation and theoretial results are alized by max values), is shown in figure 3. It an be seen that there are negative peak in both numerial and theoretial alulations. Coinident front waveforms demonstrate that the high frequeny radiation performane of atual antenna is good, so we an have lower requirement for antenna height in view of antenna parameter seletion priniple. However, the farfield pulse width alulated by simulation is far narrower than theoretial alulation. This is beause that the atual antenna length is limited and then most of the low frequeny omponents of the pulse exitation is not radiated out but returned from antenna terminal. Therefore, we have to onsider methods of impedane loading, antenna deformation, filling medium, and low frequeny ompensation loop and antenna array and so on to improve low-frequeny radiation performane for TEM horn antenna The experimental design and results analysis TEM horn antenna for experiments has length 1.5 m and height 1 m, aperture width m, two 180 ohms water resistanes are plaed at the antenna end. High voltage soure is used for harging the apaitor, and then the spark gap swith breaks over, apaitor disharges to produe an integral double exponential pulse approximately. Eletri field is measured by optial field tester, and displayed in a shielded room through the osillosope. Do gradually inrease the output voltage value to make swith breakdown. Beause of the funtional limitations of field tester, waveforms but not the field strength values are observed. E-field waveform at 5 meters shift from the aperture is shown in figure 4. In order to ompare with radiation waveform generated by double exponential pulse exitation, we an use Marx generator to replae voltage soure and apaitor, for whih far field is shown in figure 5. Figure 4. Farfield waveform with resistors at the antenna end. Figure 5. Farfield waveform with Mark generator exitation. From experimental results it an be seen that when using integral double exponential pulse exitation, far field is approximately lose to double exponential pulse form, and low frequeny radiation performane an be improved through the method of resistane loading; but when using Marx generator as exitation, TEM horn antenna atually radiate the differential form of double 5

7 7th International Conferene on Applied Eletrostatis (ICAES-01) Journal of Physis: Conferene Series 418 (013) 010 exponential pulse, and pulse width is smaller, furthermore, radiation waveform is generally in some serious osillation as the Marx generator itself output dithering double exponential pulse. Experiments indiate that TEM horn antenna an be used for radiating NEMPS, but the low frequeny radiation ability needs to be enhaned through the way of resistane loading. 5. Conlusions This paper tries to apply TEM horn antenna for NEMPS and get the following onlusions: a) Radiation theory in time domain is analyzed based on the equivalent transmission line model of TEM horn antenna with small flare angle, whih dedues far field response for the integral exponential pulse exitation, and indiates that with the antenna length and height inreasing, amplitude of radiation field beomes larger, pulse width is broaden and waveform is gradually lose to double exponential pulse form, and low frequeny radiation performane is improved, but the zero-rossing phenomena beomes serious, the part of waveform after zero goes into poor; b) Priniple for antenna parameters seletion is given as that: firstly, hoose the proper antenna length and height with taking the frequeny range into aount; and then set the struture angles based on the harateristi impedane of antenna; ) Numerial results and experimental results show that: the high frequeny radiation performane of atual antenna is good; but the narrow half peak pulse width annot satisfy the requirements. Therefore, when using TEM horn antenna as the radiating antenna of simulator, low frequeny radiation performane need to be improved. As limited by experimental onditions, the strength values of far field and field uniformity have not been analyzed. Further work will be onentrated on EMP waveform, field strength, field distribution and field uniformity and many other aspets. More importantly, we have to improve the low frequeny radiation performane of antenna through antenna optimization design in depth. Referenes [1] MIL-STD-461E 1999 [] GJB1389A [3] MIL-STD-461C 1986 [4] MIL-STD-461D 1993 [5] Baum C E 1978 IEEE. Trans. EMC 6 35 [6] Bailey V, Carboni V and Eihenberger C 010 IEEE Trans. Plasma Si [7] Bassam S, Rashed-Mohassel J 006 Piers. Online. 706 [8] Everett G 199 In: Sens. and Simul. Notes Note 340 [9] IEC [10] Todd Lee R, Glenn Smith S 004 IEEE Trans. Antennas Propag [11] Weiland T In: Int. J. Numer. model. eletron. networks, devies fields vol 9 p 95 6