Research on the Propagation of Electromagnetic Wave over the Horizon in Maritime Communication in the Atmospheric Duct Environment

Transcription

1 Reearch on the Propagation of Electromagnetic Wave over the Horizon in Maritime Communication in the Atmopheric Duct Environment Liang Chen 1, Yongxing Jin 1, Qinyou Hu 1, Kecheng Tang, Wanming Gao 1Shanghai Maritime Univerity Merchant Marine College Shanghai, China Donghai Navigation Safety Adminitration MOT Shanghai, China Abtract With the development of cience and technology, modern communication and advanced military equipment ytem increaingly rely on complex communication, electronic equipment and ytem technology, which require very high demand for broadband communication. Therefore, the propagation characteritic of electromagnetic wave in the marine atmopheric duct environment i reearched in thi paper. Baed on the introduction of the related baic knowledge of radio in atmopheric environment, the reference earth model and atmopheric tructure parameter are determined, then the multipath characteritic of the waveguide tranmiion are analyzed and modeled with the combination of PE theory and related theorie, and the lo performance of the low altitude atmopheric duct in horizontal and vertical pace i imulated. In addition, the PE method i ued to analyze the field ditribution of electromagnetic wave propagation in the waveguide, the imulation reult how that the PE analyi ha a good effect on the high frequency electromagnetic wave over GHz, and the multipath propagation in waveguide ha great advantage in long ditance communication. The reearch in thi paper get the contructive and innovative achievement in the etablihment of the multipath model, the lo performance and the viual analyi and other apect. Keyword - atmopheric duct; ray tracing;pe equation; multipath characteritic; wave lo I. INTRODUCTION Modern communication and advanced military ytem increaingly rely on ophiticated communication, electronic equipment and ytem technology, which put forward very high demand for broadband communication, o a to enure that all kind of ophiticated weapon ytem have trong urvival and attack capability in the extremely harh electromagnetic environment. Atmopheric duct i a pecial tructure that often appear in the tropophere, which generate a pecial gradient tructure of the atmopheric refractive index, thi tructure can make the propagation path of the electromagnetic wave ignal of the normal tranmiion change. Thee anomalie will lead that the radar appear blind area, and the accuracy and probability of the detection range and target location decreae everely, but it provide poibility for the realization of marine ultra long ditance communication. Atmopheric duct can interrupt the normal communication link, but alo can realize the microwave over the horizon communication of large capacity information tranmiion, o the olution of thi problem can greatly enhance the capability of the baic communication of our vat coatal area and territorial ea. In addition, in the modern war, the advantage and diadvantage of the communication ytem and the electronic countermeaure capability will directly influence the trend of the war, o it i neceary to increae the invetment in the field. At preent, reearcher in the field have carried out a lot of reearche, uch a the microwave i ued to carry out the viual communication technology and other experiment in the wave guide tructure caued by the evaporation of the ea. With the further reearch of the ea waveguide, the application of the electronic ytem which i uitable for the environmental communication of the ocean waveguide i being carried out in variou countrie. The innovation of thi paper lie in: The plane earth coordinate i creatively ued in the reearch of the waveguide, the imulation and analyi of the multipath arrival angle, time delay pread, reach height and amplitude are carried out, then the multipath model i etablihed, beide, the initial field i derived and et, and the PE method i ued to explore the adaptability of different frequencie and beyond horizon problem. In general, the reearch in thi paper get the contructive and innovative achievement in the etablihment of the multipath model, the lo performance and the viual analyi. II. RESEARCH STATUSES Atmopheric duct reearch tarted in the 1940', the national laboratory of the United State of America tudied the atmopheric duct, and the anomalou atmopheric ditribution tructure imilar to optical waveguide in the ea i dicovered through the meteorological experiment of radio wave. In the 190', the wetern reearcher carried out a lot of meteorological data collection, and obtained the meteorological tatitical parameter of the evaporation duct. U.S. reearcher ued hot air balloon and helicopter to meaure the ocean atmophere anomaly parameter, but conidering the range of ocean and the limited tet time, the experiment only atified the forecat of marine atmopheric DOI /IJSSST.a.1.B ISSN: x online, print

2 duct and the waveguide tructure. In thi period, the academic circle put forward a lot of atmopheric waveguide model, uch a the JESKE model, it ha been applied to the United State weather forecat and other ytem. Anderon ued 3GHz and 18GHz wave to reearch the evaporation waveguide, and gave the preliminary theory of the propagation mechanim in the evaporation duct (Anderon et al. 1995) [1]. Sirkova carried out the tatitical experiment of the prediction of urface waveguide lo in the outh of the United State (Sirkova et al. 003) []. Reza carried out the tet of 1.5GHz radio propagation characteritic in the Five Great Lake region of North America (Reza et al. 005)[3]. All of thee tudie have proved the feaibility of the ignal over the horizon communication in the evaporation duct. Compared with foreign mature reearch, dometic reearch tarted late. The preent reearch cope of China involve three part: one i the prediction of the atmopheric duct, including the time, the area, and the tructural parameter and o on. Two i the influence of the waveguide to the wirele communication, and the tranmiion law of the ignal in the waveguide. Three i the ue of radar in the military to earch for upiciou target. Wu Xiaojin reearched over the horizon radar and air defene application (Wu Xiaojin et al. 00) [4]. Chen Li tudied the weather characteritic of the low altitude atmopheric duct in the coatal water of China (Chen Li et al. 010) [5]. Thee achievement are more in the direction of the mechanim, formation, prediction and improvement of the atmopheric waveguide. The remainder of thi paper i organized a follow. Section 3 decribe the related theorie and key technologie: uch a refractive index, ray tracing theory, refraction theory and o on. Section 4 give the deign and contruction proce of the architecture model of the multipath characteritic of the waveguide tranmiion. Section 5 preent a real experiment to evaluate the model. Concluion i ummarized in Section. III. KEY TECHNOLOGIES A. Refractive index and refraction theory The main factor that affect the tructural parameter of the low altitude atmophere are: air temperature, atmopheric humidity, atmopheric preure, temperature and latitude, altitude, eaon and o on. Thee parameter which are cloely related to the atmopheric tructure are not only large but alo random. From the equator to the pole of the earth, the temperature will decreae with the increae of latitude []. Vertical height increae 1000 m, the atmopheric temperature reduce about.5. Over the upper tropophere, the temperature i generally table. The influence of tropophere atmophere on the tranmiion i reflected by the refraction index n. Here refractive index N i introduced. The relationhip between refractive index and index n i: n 1 10 N (1) The refractive index of tropophere air, which i compoed of a variety of dry ga and water vapor, can be expreed a: Pd e e N a b c T T T () Where Pd i the preure of dry ga, the unit i mbar. The firt item i from the contribution of no water ga, econd and third are the water vapor factor. In the range of : a 77. b 7 c (3) Thi parameter i ued in the imulation of flat earth reference [7]. h h M n1 10 N 10 N 157h a a M N 157 h (4 ) In the formula, a i the radiu of the earth, h i altitude, the unit i km. The concept correponding to M i the correct refractive index m, the relationhip between m and M can be expreed a the following form: M m110 h m1m 10 n a (5) In thi paper, M ue the flat earth ytem, and N ue the pherical earth ytem [8]. B. Geometrical optic theory in the tudy of waveguide Atmopheric refraction i a common phenomenon in nature, and the atmophere itelf i an inhomogeneou medium. So in the atmophere, the ray path of the radio wave propagation i not a traight line, but a curve or a combination of many egment of the line approximation. In thi theory, the form i a follow: nr co n0r0co0 () In the formula, r0 i the ditance from the point of departure to the earth' core, and h0 i the height of the tarting point, then r0 = R + h0. Θ0 i the angle of the ray tarting point and the level of the ground, r i the ditance from here to the center of the earth, and θ i the tangent angle of the beam to the point [9]. C. Equivalent pherical earth reference ytem The air tructure that only change with the height of the vertical i the horizontal layer. The gradient of the refraction index i defined a follow: dn g dh (7) For the tratified uniform air tructure, the refractive index and refractive index can be expreed a: DOI /IJSSST.a.1.B ISSN: x online, print

3 nn0 gh N N0 Gh (8) In the formula, n0 i the refractive index of the ray emiion point, N0 i the refractive index of the ray emiion point, and h i the altitude of the point antenna [10]. G can be called the refractive index gradient, the unit i N/km. The relationhip between the refractive index gradient g and G i: G 10 g( N km) (9) Due to the height of the antenna and the ignal propagation h i le than the earth' radiu r0, o the tranmiion of the ignal can be expreed a: 1 g h co0 1 hco (1 )co r n r Where (10) 1 re k r 1 g r0 n0 1 ke g 1 r0 n e 0 0 (11) θ0 i the angle between the ray emiion point and the horizontal line, h i the height of the point of the ray (unit: km), ke i pherical equivalent factor, re i the radiu of the effective earth urface [11]. D. Equivalent plane of the earth reference ytem In order to implify the tudy of the characteritic of the radio wave ray, the actual earth can be tranformed into a plane reference ytem in the theory [13]. On the actual earth, when the atmopheric refraction index in the pherical layered tructure i uniform, the refractive index n i only related to altitude h. Snell' law can be expreed a: h n0co0 nh1 co r0 (1) 1 h m z n z nh h r0 r0 (13) Where m(z) i the modified refraction index which determined by the high degree, m(0) = n(0) = m0 = n0,o Snell' law i rewritten a: 0 0 m co m z co (14) Figure. Plane earth model. Figure 1. Equivalent pherical model. Figure 1 i the equivalent pherical earth model, the ball O i called the equivalent pherical earth model, the equivalent radiu i re. Where S' i the pherical equivalent ytem, S i the real earth [1], TP i the actual airwave in the earth, the electric ray of equivalent pherical earth i TP, the tangent elevation angle i θ0. Baed on geometric knowledge, the launching elevation of P and P in their phere model i equal. S i the actual earth, S i the equivalent plane earth urface, S and S' i a concentric circle, circle i O. T i the launch point, TG i the horizon, O, T, K are in a traight line, which i perpendicular to TG, the length of TK, namely, the radiu difference of the two circle i h. P i the interection of S' and actual ray TP, P' i the interection of S' and equivalent ray TP'. The tangent elevation i θ0. The emiion angle of P i θ, the emiion angle of P' i the upplementary angle of θ. The elevation angle of P and P' are equal. The common external tangent of TP and TP' i TE. TE i perpendicular to CC'. In the flat earth model, the value of the m (h) i equal to the refractive index n (h) of the layered earth in the real world. So the actual earth i converted into a flat reference ytem, and the corrected refractive index i ued to replace the atmopheric refraction index. E. Ray tracing theory The ray tracing and parabolic equation are ued to reearch the atmopheric duct in thi paper. The effect of the frequency pectrum i neglected by the approximation of the ray tracing method, and the method i ued to abtract the DOI /IJSSST.a.1.B ISSN: x online, print

4 motion track of a lot of radio ray. Thi paper et the frequency i infinite, and the atmopheric denity ditribution i irregular for the ame altitude, the ray method will lead to a longer imulation time, and the uperiority of the method will drop. When the frequency i very high, the electric field of the radio ignal can be expreed a follow: E H n (15) In the electromagnetim theory: E ne (1) In thi paper, the height of the atmopheric parameter i ame, that i, n i the ame. The atmopheric environment i the only factor that influence the radio wave. Figure 3 i the pictorial repreentation tracking technique of radio wave propagation, the journey of the curve from the tarting point to a poition i l, and the ditance in a very hort period of time i ΔL. θ i the angle to the center of the earth. The atmopheric refractive index i n, θ i launching elevation. The refractive index of the new poition i n + Δn, θ i the launching elevation. Figure 3. Wave ray and the parameter of the tratified atmophere. According to the above Figure: R ndl n R R ndl R (17) It can be obtained by the Fermi principle: R R R R n R R (18) Then nrin n n R R in ' (19) That i nrin nnrr in( ) (0) Thi i the theoretical premie of the tudy of atmopheric waveguide with the method of ray. F. PE parabolic equation The parabolic equation (PE) method can decribe the field ditribution and lo model of the whole pace of the ocean evaporation duct. The pace field of the evaporation duct i expreed a β, and the wave calar equation of the β i lited under the electromagnetic field theory: fn x, z 0 x z c (1) N(x, z) i the atmopheric refractive index, i the function of the horizontal ditance and the vertical height, abbreviated a n. f i the frequency of the radio, C i the peed of light. In order to eliminate the influence of the horizontal phae hift on the radio wave propagation, the phae hift factor can be eparated into the following form: i fx ux, z x, zexp c () The u(x, z) without the ue of phae information i ued to replace the β(x, z) to decribe the amount of evaporation duct, abbreviated a u. The earth' radiu i much larger than that of the ea wave guide, and the earth model i ued to make the earth a flat urface: u u u ik k n1u 0 x z x (3) u The x can be drawn a follow: u 1 ik 1 n u x k z u 1 ik 1 n u x k z (4) When the emiion angle i very mall, the method can accurately decribe the parameter of the waveguide pace field if the energy of the backward emiion i excluded. Taylor approximation can be replaced by the following: 1 1 n 1 n k z k z (5) The calar equation can be tranformed into: u u ik k n10 z x () DOI /IJSSST.a.1.B ISSN: x online, print

5 IV. MULTIPATH MODEL OF RADIO WAVE PROPAGATION IN OCEAN WAVEGUIDE A. Ray trace of the propagation of the wave in the ea In thi paper, the waveguide trength i -1M/ meter. The 3dB width of the tranmitter antenna tranmit power i ±0.3 degree, and the waveguide tructure model i ued to trace. The premie of low altitude waveguide tranmiion ignal i that the wave are bound by the waveguide, which require that the launch elevation angle i le than the critical angle. The maximum angle correponding to the correponding trength guide can be calculated. (a) (b) Figure 4. Electromagnetic wave propagation in a waveguide with 0 ray and Multipath ray tracing of electromagnetic wave in the evaporation duct. In Figure 4, (a) repreent the electromagnetic wave propagation in a waveguide with 0 ray, (b) repreent the multipath ray tracing of electromagnetic wave in the evaporation duct. Experimental reult how that the larger the tranmiion angle, the horter the time of the radiation propagation in the waveguide, and the tructure of the waveguide layer can be pread over a more recent horizontal tranmiion ditance [14]. B. Influence of offhore evaporation duct on radio wave propagation The electric field intenity of tarting poition L1 i E1, the area i 1, and the electric field intenity of in-poition L i E, the area i. Then in the medium without conumption: 1E1 E (5) Thi paper ue the plane earth reference coordinate, the reflection of the diffuion coefficient of pherical reflection i ignored. Radio wave propagation in pace wave ha the following equation: dnne 1 1 nl 1L d n (7) Where E i the abolute value of the radio wave intenity, i the integral increae in the area of the wave, L1L i the ray path. In the imulation, the tranmiion ditance i 100 kilometer, the relationhip between the abolute value of the ignal intenity and the tranmiion ditance i: 0.5 L E 1 n exp 0.5 ldl ˆ E1 n 1 L1 (8) It how that the ditribution information of atmopheric denity and the mileage of electric wave will determine the attenuation value of electromagnetic energy expanion [15]. The reflection coefficient model i calculated: x 8 x in Re fer J0 i8 e in (9) In the formula, J0 i the Beel function, γ i the grazing angle of the ray, and λ i the radio wave length. x how that the model conider the complex ea condition of wave attenuation. In the imulation, the wave frequency and wind peed are conidered, the modified formula i: Re fer Re fer 3.t 3.t 7t9 (30) In the formula, γ i the grazing angle of electromagnetic wave repect to the ea, β i v, v i the wind peed (cloe to ea level). Refer i the water reflection coefficient, in the etting of the 4 wind peed, the parameter are calculated in the following table: TABLE I EFFECTS OF DIFFERENT SEA SURFACE CONDITIONS ON THE REFLECTION COEFFICIENT OF THE RADIO WAVE RAY wind 1m/ 4m/ 7m/ 10m/ peed β β.01e-5.58e t/inу In concluion, for the wave propagation in the waveguide, the lo i mainly compoed of energy diffuion and ea lo. Simulation reult how that the predictability of the ignal tranmitted in the waveguide tructure can be reduced rapidly becaue of the deterioration of the ea condition. DOI /IJSSST.a.1.B ISSN: x online, print

6 C. Simulation of the arrival angle of each radial waveguide The maller the angle between the ignal relative to the maximum gain direction of the antenna, the greater the gain of the antenna. Figure 5 i the imulation reult of the arrival angle. the change of the horizontal ditance, vertical height, and antenna type of the receiving antenna, and n i the time function of t. V. EXPERIMENTAL ANALYSES In thi paper, the PE parabolic method i ued to imulate the ditribution of different frequency electric field. The imulation condition: the antenna i 10 meter, the ditance from the initial field i 50 meter, the height of the evaporation duct i 0 meter, and the waveguide gradient ΔM i 0. The imulation of the wave frequency i: f = 300 MHz, f = 30 GHz, the following imulation ditance i 100 km, the capture height i 0 m. (a) (a) (b) Figure 5. Arrival angle of each path and the probability ditribution of the arrival angle of the receiver. In Figure 5, (a) repreent the arrival angle of each path at the receiving point, (b) repreent the comparion of the evaporation duct receive end angle of arrival probability ditribution and approximate normal model. Experimental reult how that the ditribution of the arrival angle of the electric wave can be approximated by a normal ditribution with a variance of D. Etablihment of the multipath propagation model of the offhore evaporation duct In thi paper, the multipath characteritic repone of the tranmiion ignal in ocean waveguide i etablihed: n reach i i delay i j Duct t E t t e i0 (31) The phyical quantity Γ i the gain graph function of receiving antenna in all direction, Ei i the ignal amplitude at the receiving antenna interval, Ψ i the wave phae.δ i the impule repone function. n will increae and decreae with (b) Figure. Simulation experiment reult. In Figure, (a) repreent the decription of the field ditribution of 300MHz wave in waveguide pace by PE equation method, (b) repreent the decription of the field ditribution of 30MHz wave in waveguide pace by PE equation method. Experimental reult how that the low frequency electromagnetic wave i difficult to achieve atmopheric waveguide tranmiion, the parabolic method DOI /IJSSST.a.1.B ISSN: x online, print

7 i not uitable for the decription of the waveguide tranmiion characteritic of low frequency ignal. VI. CONCLUSION The appearance of atmopheric duct propagation can not only caue the electromagnetic wave to deviate from the original direction of propagation, but alo can make the electromagnetic wave propagate along the waveguide to the outide of the line of ight, which eriouly affect the radar, communication, reconnaiance and other radio weapon ytem baed on electromagnetic tranmiion. How to make full ue of atmopheric duct propagation to improve the working efficiency of the electronic ytem ha important theoretical ignificance and practical value. Therefore, baed on the introduction of the related baic knowledge of radio in atmopheric environment, thi paper determine the reference earth model and atmopheric tructure parameter, and the multipath characteritic of the waveguide tranmiion are analyzed and modeled with the combination of PE theory and related theorie, then the lo performance of the low altitude atmopheric duct in horizontal and vertical pace i imulated. In addition, thi paper ue the PE method to analyze the field ditribution of electromagnetic wave propagation in the waveguide, the imulation reult how that the PE analyi ha a good effect on the high frequency electromagnetic wave over GHz, and the multipath propagation in waveguide ha great advantage in long ditance communication. Generally peaking, the innovation of thi paper lie in: The plane earth coordinate i creatively ued in the reearch of the waveguide, the imulation and analyi of the multipath arrival angle, time delay pread, reach height and amplitude are carried out. However, there are ome hortcoming. Thi paper doen t tudy the wave phae, emiion angle, Doppler Effect of the waveguide, and there i no in-depth tudy of the performance of variou frequency band radio wave in the realization of waveguide communication. Thee all are very good new direction and it can be explored later. REFERENCES [1] Anderon K D, Radar Detection of Low-Altitude Target in A Maritime Environment, Antenna and Propagation, vol. 43, No. 0, pp , [] Sirkova I,Mikhalve, Influence of Tropopheric Duct Parameter Change on Microwave Path Lo, Microwave Review, vol. 19, No. 0, pp. 43-4, 003. [3] Reza, Ray Tracing and Parabolic Equation Method in the Modeling of a Tropopheric Microwave Link, Antenna and Propagation, vol. 53, No. 11, pp , 005. [4] Chen Li, Gao Honghan, Weather characteritic of coatal water of low atmophere Chinee waveguide analyi of, vol. 38, No. 09, pp , 010. [5] Wu Xiaojin, Over the horizon radar and air defene application, modern defene technology, vol. 30, No. 05, pp , 00. [] Zhou Peng, Zhang Haiyong, He Yin, et al, Application of atmopheric duct in maritime communication, telecommunication technology, vol. 54, No. 08, pp , 014. [7] Haiyong Z, Peng Z, Chi X U, et al, Reearch on Maritime Tranhorizon Communication Ditance Baed on Evaporation Duct, Telecommunication Engineering, vol. 55, No. 01, 015. [8] Peng Z, Hai-yong Z, Yin H E, et al, Application of Atmopheric Duct in Maritime Communication, Telecommunication Engineering, vol. 54, No. 08, 014. [9] Li Lei, Wu Zhenen, Lin Leke, et al, Study on the correlation between the propagation of tropopheric microwave over the horizon and the characteritic of the atmopheric environment in the ea, Journal of electronic and information, vol. 38, No. 01, pp , 015. [10] Yinhe, Zhao Lei, Yu Sheng Zhang, During the monoon eaon in South China Sea lower atmopheric duct tatitical analyi, Journal of Radio Science, vol. 7, No. 0, pp. 8-74, 01. [11] Zhao Xiaofeng, Wang Dongxiao, Huang Sixun, et al, Statitical analyi of atmopheric duct in the South China Sea and the eatern tropical India ocean, Science Bulletin, vol. 58, No. 7, pp. 8-8, 013. [1] Zhao Chenbing, Suo Ping Zhang, Qi Zhanhui, Baed on GNSS atmopheric duct detection ytem deign and implementation, Marine technology, vol. 3, No. 04, pp , 013. [13] A Yinhe, Zhou Shengqi, Wang Dongxiao, Advance in marine atmopheric duct reearch progre, Earth Science, vol. 8, No. 03 pp , 013. [14] Xu Jinju, Study on the mechanim of electromagnetic wave propagation and radar echo in atmopheric duct, Ocean Univerity of China, 01. [15] Wang Yufei, Yan Ming, The complex electromagnetic environment of the key ea communication ecurity reearch, modern communication technology, No. 0 pp. 3-3, 014. DOI /IJSSST.a.1.B ISSN: x online, print