ON THE FUNCTIONING OF A HELICOPTER-BORNE HF LOOP ANTENNA

摘要

Numerical techniques allow engineers to evaluate the performance of antennas on complex structures. These techniques can provide valuable physical insights into the overall functional performance of such antennas. This short paper reports on the use of NEC2 to investigate the radiation characteristics of a loop antenna mounted below the tailboom of a helicopter in the frequency band 2AE15 MHz. It was concluded that such a loop antenna serves mainly to excite a dominant electrical dipole mode of operation for frequencies less than the lowest natural electrical resonance frequency of the helicopter itself, but greater than some frequency near the low end of the HF band. A limited set of measurements performed on a scale model of a helicopter generally supports the conclusions drawn from the numerical results predicted using NEC2. The reported result is of importance in so-called 'nap-of- the-earth' HF communications from helicopters. [Vol. 6, No. 2, pp. 53-73 (l99l)]