CONTROLLABLE TAKE-OFF ANGLE HIGH FREQUENCY ANTENNA

The object of this Phase I study is to optimize the radiation characteristics of antennas on board ships for improved HF (2-30 MHz) point-to-point communications. The ultimate purpose of the study is to provide an optimum shipboard antenna with variable elevation patterns and an omni-directional azimuthal pattern. For a given point-to-point circuit, the peak of the antenna radiation in elevation or Take-Off Angle (TOA) is a critical parameter in establishing a reliable HF communications circuit. A study will be made to determine 1) characteristics of typical ship-board antennas, and 2) means of adjusting the TOA of these antennas to improve HF communications at the desired ranges. The TOA characteristics of antennas as a function of polarization, height above the sea, and frequency will be investigated and correlated with the TOAs required by propagation paths for short, medium, and long-range circuits. The superstructure on the ship has a large effect upon the radiation pattern of ship-mounted antennas. This interaction will be taken into account using method-of-moments computer modeling. Innovative phasing and multi-mode excitation techniques will be investigated as a means of controlling the antenna TOA and providing an omni-directional azimuthal pattern.