System and method for selecting Doppler altered reflected signals

A method of transmitting a radio frequency signal and selecting a Doppler altered reflected signal from interfering signals comprising the steps of:

• a. transmitting noise modulated radio frequency signals;
• b. receiving Doppler altered reflected signals;
• c. heterodyning the radio frequency signals and the reflected signals to provide first heterodyne signals;
• d. altering the phase of receiving signals lying within a predetermined band of frequencies including the Doppler altered reflected signals and heterodyning the radio frequency signals and the reflected signals to provide second heterodyne signals having a predetermined phase relationship to the first heterodyne signals;
• e. amplifying the first and second heterodyne signals in broad band amplifiers to distribute the signal energy across a broad spectrum;
• f. filtering the first and second heterodyne signals in a narrow bandpass filter to pass that portion of the signal spectrum containing the Doppler frequencies and to reject the majority of the signal spectrum containing the noise modulation;
• and
• g. applying the first heterodyne signals and the second heterodyne signals to electronic circuitry which provides an output only in response to the application of two signals having the predetermined phase relationship.

A system adapted to transmit radio frequency signals and receive Doppler altered reflected signals comprising:

• a. generating means providing a radio frequency output;
• b. antenna means adapted to transmit said radio frequency output and receive reflected signals;
• c. transmission line means coupling the output of said generating means to said antenna means and receiving the reflected signals therefrom, said transmission line having first and second signal pick-off terminals positioned a predetermined number of electrical degrees apart relative to the frequency of the output of said generating means;
• d. first and second heterodyning means coupled to said first and second pick-off terminals, respectively, for providing first and second heterodyne signals each representative of the heterodyned output signal of said generating means and the reflected signal received in said transmission line, said first and second heterodyne signals having a predetermined phase relationship therebetween dependent upon the predetermined number of electrical degrees of separation between said first and second pick-off terminals and the inherent phase shift of each of said first and second heterodyning means;
• e. frequency modulation means for noise modulating said generating means, said frequency modulation means having a predetermined noise output bandwidth;
• f. first and second amplifying means for amplifying and limiting said first and second heterodyne signals, respectively, said first and second amplifying means each having an output terminal and having a bandwidth substantially equal to said predetermined noise output bandwidth of said frequency modulation means;
• g. first and second bandpass filter means for limiting the signal bandwidth from said first and second amplifying means, said bandpass filter means having a bandwidth small with respect to said predetermined noise output bandwidth of said frequency modulation means, said first and second bandpass filter means each having an input terminal connected to said output terminal of said first and second amplifying means, respectively, and each of said first and second bandpass filter means having an output terminal;
• and
• h. circuit means for receiving signals from said output terminals of said first and second bandpass filter means, said circuit means being sensitive to signals having substantially said predetermined phase relationship and providing an output in response thereto.