A Comprehensive Study on Maximum Wavelength of Electromagnetic Propagation in Different Evaporation Ducts

The maximum wavelength describes trapping features when considering electromagnetic wave propagation in an evaporation duct. However, the results vary between the existing methods used to calculate the maximum wavelength in an evaporation duct. Hence, this study provides a comprehensive analysis of the maximum wavelength of electromagnetic propagation in an evaporation duct. First, the existing methods are introduced and the differences between these methods are discussed. Second, the frequency responses from 1 to 20 GHz of the evaporation duct channel are analyzed. The trapping features of different evaporation duct channels are investigated. Based on the frequency responses, the existing methods are compared and evaluated. Finally, the frequency response of the evaporation duct channel was measured in the South China Sea along a 149-km-long propagation path in 2014. The data collected in the experiment are used to verify the conclusion. Both the simulation and experimental results show that the Kerr's method and Kukushkin's method do not represent the cutoff conditions for electromagnetic propagation, while Brekhovskikh's method and Hall's method can calculate the maximum wavelength in an evaporation duct. The recommended value k for using the Turton's method is also given.