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]. γ o = = 6.6 2 +0.33 + 9 −57 2 +1.96 2 10 −3 (1) = 0.067 + 2.4 −22.3 2 +6.6 + 7.33 −183.5 2 +5 + 4.4 −323.8 2 2 10 −4 (2) = + (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] 555