Divergent beam shaping for high data-rate underwater communications

High data rate underwater communication systems remain elusive. High frequency propagation combined with a frequency re-use appears to be a viable means to achieve high data rate underwater networks. However the required low-cost, high-frequency, omni-directional transducers with reasonable power handling capabilities do not exist. Small transducers cannot handle power, but large devices become directional at increasing frequency. Small transducers are also likely to be expensive because of manufacturing tolerances. We propose and investigate using a divergent reflector to transform a narrow beam into a donut shaped radiation pattern. The anticipated beam shape from a reflector is modelled using ray tracing techniques. A prototype reflector is then constructed and tested in still fresh water, showing the ability of a reflector to shape the reflected beam in an appropriate pattern. Testing on a spar buoy in salt water confirmed the signal is radiated laterally and provides a consistent signal even between typical floating platforms.