Over-the-Horizon Propagation Characteristics of the Coupled Evaporation Duct and Tropospheric Scatter Channels at Different Frequencies and Antenna Heights

The evaporation duct and tropospheric scatter significantly influence over-the-horizon (OTH) electromagnetic wave propagation. In the intricate marine atmospheric setting, these phenomena tend to occur simultaneously. However, most studies tend to examine them separately. This research uses the parabolic equation model to investigate microwave propagation characteristics close to the sea surface when both evaporation duct and tropospheric scatter are present. The results show that the coupled channel structure captures more microwave energy and reduces path loss compared to cases considering only one mechanism. Moreover, we simulate electromagnetic wave propagation characteristics across various microwave frequencies and antenna heights. When the evaporation duct height (EDH) is below 7 m and frequencies exceed 3 GHz, tropospheric scatter mitigates the limitations of the evaporation duct, resulting in approximately a 100 dB decrease in path loss within the coupled channel. Taking tropospheric scatter into account under these circumstances can effectively lower the path loss of the coupled channel. This research reveals coupled channel propagation characteristics and provides theoretical insights for optimizing OTH communication systems.