Doppler tracking processor and time of closest approach detector

Abstract

Disclosed is a Doppler tracking processor and time of closest approach detector for use in active or semiactive radar-guided missiles. A known processor uses a fractional Doppler gate (FDG) to process the Doppler signal to activate the warhead detonation properly at time of closest approach (TCA); it indicates when the Doppler energy has rolled off to, for example, one-half the pre-intercept Doppler frequency. The present invention uses a Doppler tracking processor and TCA detector. The tracking filter can extract the instantaneous value of the Doppler frequency even during rolloff. The system processes the Doppler from the preintercept frequency up to an appropriate fractional frequency occurring at TCA, at which time it provides a signal for use in warhead detonation.

The embodiments of the invention in which an exclusive property or privilege is clained are defined as follows: 
     
       1. A Doppler tracking processor and time of closest approach detector system comprising: first means for deriving a reference signal proportional to a predetermined fraction of the frequency of a Doppler signal, said first means comprising a fractional ratio converter having an input to receive a voltage proportional to the Doppler signal, said converter having filtering and attenuation means for deriving said reference signal from said voltage;   second means for deriving a second signal which is dynamic and is proportional to the instantaneous Doppler frequency of the Doppler signal during Doppler roll-off; and   comparator means for comparing said second signal and said reference signal, said comparator producing an output signal if said second signal drops below said reference signal.   
     
     
       2. A system as claimed in claim 1 wherein said second means comprises a tunable band-pass filter having a first input to receive said Doppler signal, a control input, and an output, said output being connected to the input of a feedback loop having an output connected to the control input of the tunable band-pass filter. 
     
     
       3. A system as claimed in claim 2 wherein the output of the feedback loop is also connected to a low-pass filter, said low-pass filter having an output connected to said comparator. 
     
     
       4. A system as claimed in claim 3 wherein said feedback loop comprises a fast automatic gain control circuit followed by a fast frequency-to-voltage converter. 
     
     
       5. A system as claimed in claim 4 further including means for scaling said reference signal to the output of the frequency-to-voltage converter. 
     
     
       6. A system as claimed in claim 5 further including means for continuously tuning the tunable bandpass filter over the 5-150 kHz band. 
     
     
       7. A system as claimed in claim 6 wherein the feedback loop includes means for adjusting the center frequency of the tunable band-pass filter to keep its bandpass center frequency in substantial coincidence with the component of greatest amplitude in the Doppler signal.