Electromagnetic field radiated in air from a horizontal/vertical magnetic dipole in sea

The propagation characteristics of electromagnetic (EM) waves across the seawater-air interface influence seawater to air communication. The type of underwater antenna determines EM wave propagation performance. However, studies rarely compared the performance of horizontal and vertical magnetic dipoles (HMD and VMD). In this study, the EM fields in air due to HMD/VMD immersed in sea were derived to provide a basis for selecting a suitable underwater antenna for EM wave propagation in undersea-air communication. Analytic results were obtained from the model of a three-layered conducting media. Associated expressions in air were numerically calculated using the fast Fourier Transform algorithm to present the propagation curves and the distribution patterns of the EM fields. A proof of concept measurement system was constructed, and sea experiments were conducted and compared with theoretical studies. The maximum transmitting-receiving distance in the experiment was achieved by the HMD. The theoretical and experimental results indicate that the HMD antenna is superior to the VMD antenna and that the suggested band of EM wave is feasible for transmission across the seawater-air interface.