Radiation characteristics of a ship-mounted high frequency ground wave radar antenna

Ship-mounted groundwave radar (GWR) systems can be used to detect over-the-horizon icebergs, ships and low flying aircraft. Due to space limitations, vertical quarter-wave monopoles mounted on top of the irregularly shaped conducting ship structure or half-loop monopoles mounted on either side of the ship´s side hull are usually considered good candidates for this application. Both the moment method and the geometrical theory of diffraction are used to calculate the in situ far field radiation patterns of these two types of GWR antennas. The objective of this investigation is to evaluate the far field radiation pattern taking into account all field components including geometrical optics, diffraction produced by surrounding edges and corners and dominant diffraction/reflection interactions. The results indicate that the ship´s geometry can have a considerable impact on the radiation patterns of its on-board antennas. For example, the omnidirection horizontal radiation pattern of a vertical whip monopole over a perfect ground can be deformed to a pattern with a 17/spl deg/ beam width main lobe and a 15 dB front-to-back ratio for specific locations on the ship.