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

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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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