Detection of targets in the presence of clutter using target echo modulations caused by rotating structures

The radar detection of hovering helicopters in the presence of clutter was investigated. It is shown that radar backscatter modulation by helicopter rotors can be described as line spectra in the frequency domain, with the spacings equivalent to the product of the rotor rotation frequency and the number of rotor blades. Typical values are between 10 and 40 Hz. Experimental results obtained with a coherent E-band pulse Doppler radar are in good agreement with calculated values. Based on these results, a detector which allows the detection of hovering helicopters in the presence of clutter is proposed. The required radar parameters, such as radar dwell time and radar pulse repetition frequency, are discussed.