Floating Hemispherical Helical Antenna for Ocean Sensor Networks

Floating wireless sensor networks present unique communications challenges. Monopole and loop antennas have been used in seawater; however, a hemispherical antenna has the advantage of an increased efficiency and propagation range compared to other designs. This paper reports the design, construction, testing, and simulation of a hemispherical antenna and its propagation across the sea surface. Antenna modeling shows a return loss of -15 dB and a radiation efficiency of 57% in a partially submerged condition. The modeled and measured bandwidths were 47% and 36%, respectively. The radiation pattern corresponds to that of a vertical monopole antenna, when the hemisphere is floating on the water surface. Propagation range measurements in a calm coastal bay showed two separate attenuation trends of 2 dB/m and 4 dB/m, before and after the reference distance (40 m), respectively. The link range was greater than 135 m using a transmit power of 10 dBm and a receiver sensitivity of -100 dBm. Results show that the floating hemispherical antenna can be successfully deployed and used in wireless sensor network applications for coastal areas.