Effects of Near-Field Obstacles on Far-Field Antenna Performance Characteristics

Considerable research has been conducted to investigate near-field coupling between antennas, both with and without obstacles located in the near-field of the antennas, but until now, very little research has been conducted to provide information for predicting the effects of various near-field obstacle blockages on far-field antenna performance characteristics. Recently completed research investigations at Georgia Tech for the U. S. Naval Ship Engineering Center have yielded considerable design information and have provided much insight into potential problem areas such as those dealing with nearfield obstacles and their effects on far-field gain loss, beamwidths, beamshifts, and maximum sidelobe levels. The effects of several variables on these far-field antenna performance characteristics were investigated, and various trends as well as typical design curves will be discussed. The usefulness of the information is illustrated by insertion of the far-field gain-loss data into a computer program for shipboard siting of antennas. Moreover, based on theoretical and experimental investigations with a dielectric-coated solid metal circular mast, applications of dielectric coatings to portions of ship superstructures to improve the far-field antenna performance is possible. A correlation of the effects of near-field obstacles on far-field antenna characteristics and on near-field antenna-to-antenna coupling is also possible.