The moving parts of an aircraft, such as rotor blades, propeller blades, and jet engine compressor and turbine blades, cause a periodic modulation on the radar return signals. Though this periodic modulation can sometimes effect the Doppler tracking of the target, it can also provide important information for target identification as a radar signature. The phenomenon of the spectrum envelope modulation is analyzed in terms of electromagnetic scattering computation and experimental results of rotating blades. The results show that the blade twist is one of the important factor that impacting the spectrum distribution.
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