Method for Compensating Helicopter Main Rotor Signal in the Time Domain Before Constructing a Tail Rotor Radar Image

Introduction. The most common helicopters are those based on a single rotor design, each with a main rotor and a tail rotor. Radar images of helicopter rotors, combined with their rotational speeds, contain information that allows the helicopter type to be determined. The amplitude modulation law for signals reflected from the main rotor blades is of a pulse nature. These modulation pulses significantly exceed the amplitude of the signal reflected from the airframe. Therefore, constructing an image of the main rotor presents no fundamental difficulties. However, the amplitudes of signals reflected from the tail rotor blades are significantly smaller than those of the main rotor. Therefore, the problem of measuring the rotational speed of the tail rotor blades against the background signal of the tail rotor is not solved. Consequently, the problem of constructing an image of the tail rotor is not solved. This problem is additionally complicated by the overlapping spectra of the signals reflected from the main and tail rotors.

Aim. Development of a method for compensating the helicopter rotor signal in the time domain.

Materials and methods. Compensation for signals reflected from main rotor blades can be accomplished through various approaches. This paper discusses a method based on the use of complex amplitude moduli of reference signals in the main rotor imaging channel. These moduli are used to generate a time-domain weighting function for signals reflected from the main rotor blades. This function, by weighting the received signal, ensures compensation for reflections from the main rotor blades.

Results. A method for compensating for the helicopter main rotor signal in the time domain has been developed for constructing a radar image of the helicopter tail rotor. The method does not require extensive computational resources. Its effectiveness is illustrated using a signal reflected from an Mi-8 helicopter as an example.

Conclusion. The developed method enables compensation for signals reflected from the blades of the helicopter main rotor and creates conditions for measuring the rotation frequency and constructing an image of the helicopter tail rotor. 

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