Range detector

A range determining system including in combination, transmitter means for producing pulses of high frequency oscillations and including antenna means for radiating and receiving said pulses, means coupled to said antenna for selecting said pulses after reflection with the reflected pulses having Doppler frequency components produced by relative movement between said antenna means and the reflecting object, first mixer means for reducing the frequency of the oscillations of the received pulses, second mixer means coupled to said transmitter means for reducing the frequency of the oscillations of the transmitted pulses, first delay means connected to said second mixer means, a first zero beat mixer having inputs connected to said first mixer means and to said first delay means for deriving the Doppler frequency components from reflected pulses which have a delay corresponding to the delay of said first delay means, second delay means connected to said first delay means, a second zero beat mixer having inputs connected to said first mixer means and to said second delay means for deriving the Doppler frequency components from reflected pulses which have a delay corresponding to the sum of the delays of said first and second delay means, first and second bandpass filter means each including limiter means for providing gain control and connected to the outputs of said first and second zero beat mixers respectively for selecting the Doppler frequency components within a given band, multiplier means connected to said first and second filter means for multiplying the signals therefrom, low pass filter means connected to said multiplier means for selecting signals below a given frequency, and peak detector means connected to said low pass filter for producing an indication when the signals from said first and second bandpass filter means are of the same frequency.