Spectral characteristics of electromagnetic wave scattering by rotating propellers and its effect on clutter discrimination

On aircraft that are propeller driven, the transmitted electromagnetic (EM) signal which emanates from a transmitting array on the aircraft is modulated, both spatially and spectrally, by the rotating propellers. The spectral effect is to introduce a discrete frequency spread (about the monotonic transmitted carrier frequency) to the propeller scattered fields. These additional spectral lines result in additional competing clutter patches at various cone angles for a given Doppler bin. If one is doing space time adaptive processing (STAP), the existence of these additional clutter patches at different cone angles require pattern suppression in each of the directions of clutter return. The extent to which this modulation modifies the intended transmitted waveform is an issue that can have serious ramifications on the overall system performance. The computational approach used is to consider the motion of the propeller as a succession of stationary snapshots to examine the radiation field variation. The method of moments (MoM) was used for examining the fields scattered from stationary propellers.<>