초록 ▼

An airborne pulse doppler radar set generally includes a moving target indicator (MTI) system for detecting moving aircraft within its scanning purview. To avoid processing undesirable clutter, the MTI system includes a clutter cancelling type filter for rejecting doppler shift frequency signals ref

An airborne pulse doppler radar set generally includes a moving target indicator (MTI) system for detecting moving aircraft within its scanning purview. To avoid processing undesirable clutter, the MTI system includes a clutter cancelling type filter for rejecting doppler shift frequency signals reflected from objects moving at velocities below a predetermined minimum velocity value. Unfortunately, the doppler shift frequencies representative of the body velocity of most helicopters fall within this clutter repetition band and may go undetected by the MTI system. To detect these helicopters, a helicopter detection system which operates on the specular flash energy of the doppler shift frequency signals reflected from the rotating blades of a helicopter is provided. The helicopter detection system passes substantially the received reflected radar signals that have doppler shift frequencies representative of the helicopter rotating blade velocities, derives a threshold value based on the values of the passed signals, and generates detection signals at times corresponding to the passed signal values which are at least that of the derived threshold value. In addition, the helicopter detection system is capable of inhibiting the generation of the detection signals at time corresponding to the reception of interference type radar signals by the radar set. Furthermore, an unambiguous range of each detected helicopter may be computed. Moreover, the helicopter detection system has the capability of distinguishing between detected targets having even and odd numbers rotating blades.

대표청구항 ▼

A helicopter detection system for the radar detection of helicopters having at least one rotor blade rotating within a predetermined velocity band, said system including: a radar transmitting unit for transmitting radar energy pulses at at least one predetermined pulse repetition frequency within a

A helicopter detection system for the radar detection of helicopters having at least one rotor blade rotating within a predetermined velocity band, said system including: a radar transmitting unit for transmitting radar energy pulses at at least one predetermined pulse repetition frequency within a scanning purview; a radar receiving unit for receiving transmitted radar signals which are reflected from objects within said radar transmission scanning purview, said received reflected radar signals including the doppler shift frequency signals of the corresponding reflective objects; a radar clutter filtering means coupled to said receiving unit, for rejecting substantially doppler shift frequency signals of the received signals which fall within predetermined frequency bands so as to prevent further processing of said rejected signals, the reflected doppler shift frequency signals which are representative of the body velocity of said helicopter being within at least one of said predetermined doppler shift frequency bands; a first doppler processor operative to detect the doppler shift frequency signals representative of a helicopter blade rotating in a first direction with respect to said radar transmission at a velocity in said predetermined velocity band and to provide a first signal indicative of said detection; a second doppler processor operative to detect the doppler shift frequency signals representative of a helicopter blade rotating in a second direction with respect to said radar transmitter at a velocity in said predetermined velocity band and to provide a second signal indicative of said detection; and means responsive to said first and second signals to generate a third signal indicative of the presence of at least one helicopter in the scanning purview of said radar transmitter.