The authors describe the analysis that was conducted using the NEC3-method of moments code to predict the input impedance and far-field patterns of two types of HF antennas for the US Coast Guard HH-60J helicopter. The operating frequencies for these antennas are 3.123, 5.696 (primary frequency), 8.984 (secondary frequency), 11.201, and 15.084 MHz. The calculated results have been validated by comparison with measurements on the real helicopter as well as on a 1:7.5 scaled down model of the helicopter. The impact of tuning reactance on the radiation efficiency of the antennas, as well as the relative performance of the two antennas for high angle sky wave and ground wave communications over mixed land and sea paths, has been investigated.
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