An HF Channel Measurement Testbed for Underwater/Under-Seawater Communications

The authors constructed a testbed for underwater/under-seawater radio wave communication, consisting of a transmitter, a receiver, transmitting and receiving antennas, a lock-in amplifier, and other apparatuses. It is controlled from the water surface via an optical cable, enabling us to neglect the unwanted EM coupling between transmitting and receiving antennas through conductive power and control cables. The antennas comprise of one-turn loops combined with a buffer layer structure. The buffer layer was filled with an optimized transmission medium which has a relative permittivity between freshwater and air. In the proposed system, the propagation losses decreased compared to theory; therefore, received signals (-50dB) at an HF band were detected up to 4 m in water.