Tactical HF communication for military helicopters using the NVIS mode

The use of loop antennas for tactical HF communications on board of military helicopters was investigated. The helo platform is considered for land or maritime scenarios. The experiments on the SH-3D helicopter compared the loop antennas and existing wire antennas. Groundwave radiated field at different azimuth angles were measured for the two antenna types, particularly at the lower end of the frequency range where the difference in the antenna geometry is more significant. A consistent better performance of the loop over the wire, typically a 16 dB to 8 dB improvement is indicated. Skywave propagation tests at different distances and altitude of the helicopter were conducted. It is found that the performance of the loop antenna is superior to the wire. It is concluded that the loop antenna is an ideal radiator for use onboard aircraft and helicopters because of its dimensions, increased efficiency, and radiation characteristics.