2.4 GHz Radio Transmission Measurements in a Basin filled with Sea Water
Résumé
Measurements of scattering parameter around 2.4 GHz have been presented for dedicated aligned immersed antennas in two experimental basins, one filled with fresh, the other with sea water. The measurements demonstrate transmission capabilities of these low cost antennas to support 54 Mb/s Wi-Fi underwater communications over short distances (25 cm in fresh water, 10 cm in sea water), using low emission power (10 dBm) and standards Wi-Fi modems. When salinity of water is changed from 0 (fresh) to 4 S/m (sea), only the range of transmission is affected, not the functioning of the developed antennas [3]. Moreover experiments confirmed that for a given separation distance, the rotation of one antenna around the transmission axis does not impact the signal level received (polarisation alignment unnecessary). Variation of reception due to misalignment is also reported in the case of fresh water. Otherwise multiplying the emitting power by a factor 10 will increase the range by about only 3,5 cm in fresh water and 1 cm in sea water (2.4 GHz, 20°C). Impact of bio pollution on antenna performances as well as their integration in real underwater systems should now be considered, as well as the extension of their application areas. Their compactness and bandwidth can be further improved.