Rotor-blade modulation on antenna amplitude pattern and polarization: predictions and measurements

The rotation of lift- and thrust-generating airfoils causes a periodic variation in aircraft communication signals. This effect is called rotor-blade modulation (RBM). The RBM on the radiation characteristics of helicopter-mounted antennas are predicted using the uniform theory of diffraction (UTD) and the finite-difference time-domain (FDTD) method and are compared with scale model measurements and full-scale in-flight measurements. In addition, the effects of electric field polarization on RBM are studied using the FDTD.