Helicopters have become carriers of several transmitting and receiving antennas for information exchange with other aircrafts, satellites or ground stations. The finite-difference time-domain, the finite element method and the method of moments were used to investigate some major issues in helicopter communications in the high frequency (HF) and very high frequency (VHF) bands. Input impedance and radiation patterns, antenna coupling, rotor modulation and ground effects were computed. Rotor-blade rotation was found to significantly affect the gain patterns of an HF towel-bar antenna especially at resonant frequencies. Also, ground may reduce the gain of a VHF antenna for elevation near grazing and zenith.