HF antennas for NVIS applications mounted to helicopters with tandem main rotor blades

Radio communication via Near Vertical Incidence Skywave propagation: an overview

“…5d. Similar NVIS loop antennas may be designed for transport aircraft [20], helicopter [64] and ships. Due to its increased size, the shipboard loop in [65] achieves an NVIS antenna gain between −1 and +4 dBi between 2 and 7 MHz.…”

“…Due to its increased size, the shipboard loop in [65] achieves an NVIS antenna gain between −1 and +4 dBi between 2 and 7 MHz. In helicopters, the antenna designer has to prevent unwanted modulation of the signal by the rotating rotors [64,66].…”

Near vertical incidence skywave

“…This antenna is depicted in Figure 2.6. Similar NVIS loop antennas have been designed for transport aircraft [Cummings, 2005], helicopter [Richie, 2003] or ships. Due to its increased size, the shipboard loop in [Vlasic, 2008] achieves an NVIS antenna gain between -1 dBi and +4 dBi between 2 MHz and 7 MHz.…”

“…Due to its increased size, the shipboard loop in [Vlasic, 2008] achieves an NVIS antenna gain between -1 dBi and +4 dBi between 2 MHz and 7 MHz. In helicopters, the antenna design has to consider modulation of the signal by the rotating rotors [Polycarpou, 2000;Richie, 2003]. [Barker, 1971] and [Austin, 2002].…”

“…The optimization of the vertical radiation diagram of such antennas remains a challenge, due to the radiation of currents induced in the vehicle body [Austin, 1994]. On large helicopters, these currents may cause unwanted rotor modulation on specific frequencies [Richie, 2003]. On the other hand, these current can be used effectively by creating an NVIS slot antenna in the body of an airplane [Saakian, 2012].…”