Radar signatures of rotor blades

Rotation of rotor blades in a helicopter modulates the phase function of radar backscattering, induces frequency modulation on returned signals, and generates side-bands about the center frequency of the helicopter's body Doppler frequency. The modulation induced by rotations can be regarded as a signature of the interaction between the rotor blades and the body of the helicopter, and provides additional information for target recognition complementary to existing recognition methods.