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Prediction of Electromagnetic Wave Propagation
in Dispersive Atmospheric Environments
Changseong Kim, Jun Heo, Daeyeong Yoon, and Yong Bae Park Department of Electrical and Computer Engineering, Ajou University, Suwon
Abstract – We predict the electromagnetic wave propagation
in dispersive atmospheric environments. Refraction and
reflection of electromagnetic waves in the atmosphere are mainly due to dispersive troposphere and ionosphere. Attenuations in troposphere and ionosphere are calculated
using the effective refractive index and ITU-R P.531 data, respectively. The path loss from the earth to an observation point is computed using ray tracing technique and geometrical
optics to illustrate the characteristics of wave propagation in dispersive atmospheric environments.
Index Terms — dispersive atmosphere, complex refractive
index, ray tracing technique, geometrical optics.
1. Introduction
Prediction of electromagnetic wave propagation in
atmosphere is an important issue in satellite communications.
The space environment consists of the atmosphere and the
vacuum atmosphere. EM wave propagation through the
atmosphere is affected by variations in the refractive indices
of each atmospheric layer. The refractive index depends on
the altitude, and the EM wave is reflected, refracted, and
attenuated when it propagates through the atmosphere. The
refractive index also depends on frequency[1]. Thus, the
dispersive atmospheric environments should be considered to
predict wave propagation in the atmosphere
In this paper, we study the electromagnetic wave
propagation in dispersive atmospheric environments. We use
the ray tracing technique and geometrical optics to calculate
path loss in troposphere[2]. Attenuation in troposphere is
calculated using the dispersive effective refractive index.
Attenuation in ionosphere is computed using ITU-R P.531
recommendation, which has the dispersive ionospheric
absorptions, refraction, and scintillation data [3].
2. Properties of Troposphere and Ionosphere
In the troposphere, electromagnetic wave is considered
through changes in refractive index. Real part of the
refractive index is used for refraction and reflection
calculations, and the imaginary part of the refractive index is
used for tropospheric absorption calculations [4]. Using the
weather information from the University of Wyoming, We
can calculate real part of the refractive index [5]. The
imaginary parts of complex refractive index can be
calculated using the total attenuation. The total attenuation is
computed by equations (1)-(3) in [6], [7].
γo = 𝛾𝑜 = 6.6
𝑓2+0.33+
9
𝑓−57 2+1.96 𝑓210−3 (1)
𝛾𝑤 = 0.067 +2.4
𝑓−22.3 2+6.6+
7.33
𝑓−183.5 2+5+
4.4
𝑓−323.8 2 𝑓2𝜌10−4(2)
𝐴𝑎𝑖𝑟 = 𝛾𝑜 + 𝛾𝑤 𝑟𝑜 (3)
Fig. 1 shows imaginary parts of dispersive complex
refractive index of atmosphere on ground surface of Osan,
South Korea. The imaginary refractive index has the largest
value around 24GHz, the resonant frequency of water vapor.
Fig. 2 illustrates the complex refractive index versus altitude
from 0 to 30 km. As the altitude increases, the complex
refractive index decreases to 1.
Fig. 1. Imaginary refractive index of air vs frequency (0 km)
(May 21, 2018, Osan, South Korea.)
Fig. 2. Atmospheric refractive index vs altitude (10 GHz)
(May 21, 2018, Osan, South Korea.)
2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea
[FrG3-6]
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Since the ionosphere is ionized by solar radiation,
electromagnetic waves undergo refraction, reflection, and
scintillation. Because the ionosphere is an inhomogeneous
medium and its fluctuations occur quickly, it is difficult to
analytically solve the wave equation. Thus, we use
propagation information to approximate ionospheric effects.
ITU-R P.531 recommendation provides dispersive
ionospheric absorptions, refraction, and scintillation data.
3. Path Loss Calculation
We use the ray tracing technique and geometrical optics to
calculate path loss in troposphere. Attenuation in troposphere
is calculated using the dispersive effective refractive index.
Attenuation in ionosphere is computed using ITU-R P.531
recommendation, which has the dispersive ionospheric
absorptions, refraction, and scintillation data. Fig. 3 shows
atmospheric path loss compared with the free space path loss.
The observation point is 400 km from the earth. Below 10
GHz, ionospheric attenuation is larger than the tropospheric
attenuation. Above 10 GHz, however, tropospheric
attenuation is larger than ionospheric attenuation.
Fig. 3. Path loss considering atmospheric environments
4. Conclusion
We have predicted electromagnetic wave propagation in
dispersive atmospheric environments using the ray tracing
technique and geometrical optics. We have considered the
dispersive refractive index in troposphere and ITU-R P.531
recommendation for ionosphere to calculate path loss from
the earth to the observation point at low earth orbit. Our
high frequency approximation method is useful to predict
electromagnetic wave propagation for an actual-size earth
space model.
Acknowledgment
This work was supported by the research fund of Signal
Intelligence Research Center, supervised by the Defense
Acquisition Program Administration and Agency for
Defense Development of Korea.
References
[1] Van Vleck, J. H, “The Absorption of Microwaves by Uncondensed Water Vapor”, Physical Review, 71.7 (1947): 425
[2] Changseong Kim, Yong Bae Park, “Prediction of Electromagnetic Wave Propagation in Space Environments Based on Geometrical
Optics”, Journal of Electromagnetic Engineering and Science, vol. 17,
no. 3, pp. 165-167, 2017 [3] Series, P. “Ionospheric propagation data and prediction methods
required for the design of satellite services and systems”,
Recommendation ITU-R P.531-13, 2016 [4] Hans J. Liebe, “Modeling attenuation and phase of radio waves in air
at frequencies below 1000 GHz”, Radio Science, 16(6), pp 1183-1199,
1981 [5] University of Wyoming, Department of Atmospheric Science,
"Atmospheric soundings," [Online]. Available:
http://weather.uwyo.edu/upperair/sounding.html [6] Recommendation ITU-R P.676-11, “Attenuation by atmospheric
gases”, ITU-R Recommendations, ITU, 2016
[7] Louis J. Ippolito Jr, Radiowave Propagation in Satellite Communication, Van Nostrand Reinhold Company Inc., 1986
2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea
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