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

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