An apparatus designed to measure field patterns of circular-loop antennas immersed in fresh water is described. Measured field patterns are presented to show the differences between bare and insulated loop antennas and to compare loops having different forms of insulation. The insulation is seen to alter the field pattern significantly when the loop dimensions are such that it is electrically large in the water but not in dielectric material forming the insulation. Some shaping of the field pattern can be accomplished by placing the wire loop asymmetrically in the insulation. The measured field patterns are in good agreement with theoretical patterns calculated using the Fourier series analyses for bare and insulated circular-loop antennas.
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