Abstract: The effects of helicopter rotor-blade modulation on the electromagnetic behavior of HF antennas mounted on the airframe are analyzed by method of moments (MoM) with fast multipole method (FMM) based on a surface patch model. By 3D computer aided modeling, a full size model is constructed and the surface meshing of the model is accomplished automatically. Based on these techniques, the modulation effects of rotating blades on the magnitude and frequency of the antenna radiation field are calculated by the quasi-stationary method in combination with fast Fourier transform (FFT) algorithm. Furthermore, the variation of the input admittance and mutual admittance of the antennas are analyzed when the blades rotate. The computed results show that the antenna radiation field is interfered severely by the rotating blades. These techniques can also be used to the investigations on the electromagnetic behavior of antennas mounted on other types of helicopters and platforms with rotating blades.

Key words: helicopter, rotor-blade modulation, 3D computer aided modeling, line antenna, electromagnetic radiation, method of moments, fast multipole method, quasi-stationary method