Design of horizontal magnetic dipole for HF communications

In high-frequency (HF) frequency band radio waves can propagate over a few thousand kilometers owing to the reflection from ionosphere. In doing so, the ionosphere channel constitute an alternative to satellite communications when smaller data rates (bandwidths) are of interest. The entire range of distances can be covered if an antenna system supports all three modes of propagation: near vertical incidence skywave (NVIS), long range skywave and surface wave. Design of antennas for NVIS mode is the most challenging since they have to operate over the low end of HF frequency band. Due to size constrains, these antennas are electrically small, and thus they are inherently narrowband and have small radiation resistance. In addition, antenna pattern should have maximum at zenith, though there is no stringent requirement for the signal polarization.