RANGE-GATED DIGITAL AMTI SYSTEM

• US 3,778,828 A
• Filed: 02/27/1967
• Issued: 12/11/1973
• Est. Priority Date: 02/27/1967
• Status: Expired due to Term

• Current Assignee: Wilmer H. Mcfarland
• Original Assignee: Wilmer H. Mcfarland
• Inventors: McFarland, Wilmer H.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US04/618,823
• Time in Patent Office: 2,479 Days
• Field of Search: 343/5DP,7.3,7.7 328/151,165
• US Class Current: 342/161
• CPC Class Codes: G01S 13/534 based upon amplitude or phase shift resulting from movement of objects, with reference to the surrounding clutter echo signal, e.g. non coherent MTi, clutter referenced MTi, externally coherent MTi
• CPC Class Codes: G01S 13/64 Velocity measuring systems using range gates

Abstract

A pulsed energy system for airborne use and having range-gated digital means for doppler processing of moving-target signals. A digitizer generator provides a first pulse train, indicative of the video output of the system receiver, as an up-count input to an up-down counter. An adjustable pulse train, (corresponding to the function Vacos theta ) is applied as a down-count input to the up-down counter. A synthetic video, or display, signal is gated-on in response to an overflow condition of the up-down counter.

Claims

1. In a video sampled data system, digital filter means for indicating the presence of a spectral component in the video envelope of the output of said system and above a preselected lower limit frequency, and comprising:

digitizer means responsive to the amplitude and sampled interval of the sampled video of said system for providing a pulse output indicative of a non-zero frequency component of said video envelope;

periodic pulse generating means having a periodicity correspOnding to a selected lower limit bandpass frequency; and

an up-down counter having an up count input responsive to the output of said digitizer means and a down count input responsive to the output of said pulse generating means for generating an over flow condition indicative of the presence of a video envelope spectral component in the frequency region above said lower limit frequency.

2. The device of claim 1 in which the periodicity of said periodic pulse generating means is adjustable, whereby said selected lower limit bandpass frequency is correspondingly adjusted.

3. In a video sampled data system, digital filter means for indicating the presence of a spectral component in the video envelope of the output of said system and above a preselected lower limit frequency, and comprising:

a digitizer means responsive to the amplitude and sampled interval of the sampled video of said system for providing a pulse output indicative of a non-zero frequency component of said video envelope above a preselected threshold amplitude;

periodic pulse generating means having a periodicity corresponding to a selected lower limit bandpass frequency; and

an up-down counter having an up count input responsive to the output of said digitizer means and a down count input responsive to the output of said pulse generating means for generating an overflow condition indicative of the presence of a video envelope spectral component in the frequency region above said lower limit frequency.

4. In a periodically sampled video signalling system, a bandpass limited digital filter having an upper and a lower cut-off frequency and comprising digitizer means responsive to the sampled video signal and to the sampling periodicity of said signalling system for providing a pulse train indicative of a non-zero-frequency spectral content of said sampled video signal less than one-half the frequency at which said sampled video signal is sampled;

and synthetic video means responsive to said sampling periodicity and to said non-zero-frequency pulse train for providing an output pulse in synchronism with said sampling periodicity.

5. The device of claim 4 in which said synthetic video means includes means for limiting the lower cut-off frequency of the bandpass of said digital filter and comprising a reference periodic pulse generator having a frequency less than one-half the sampling frequency of said sampled signalling system and corresponding to a lower limit frequency of the bandpass of said filter;

an up-down counter having an up-count and a down-count input, one of said inputs being responsive to a pulse train output of said digitizer and a second input responsive to a pulse train output of said reference pulse generator; and

coincidence signalling means responsive to said sampling periodicity and a preselected condition of said counter for generating an output signal.

6. The device of claim 5 in which the frequency of said reference periodic pulse generator is adjustable, whereby said lower cut-off frequency of said digital filter may be correspondingly adjusted.

7. The device of claim 6 in which there is further included means for varying the frequency of said reference periodic pulse generator as a function of the velocity of a utilizing vehicle.

8. The device of claim 6 in which there is further included means for varying the frequency of said reference periodic pulse generator as a function of the look angle of a utilizing sensor system.

9. The device of claim 6 in which there is further included means for varying the frequency of said reference periodic pulse generator in accordance with the product of vehicle velocity and cosine of sensor look angle of a utilizing sensor mounted on a moving platform.

10. The device of claim 4 in which said digitizer includes means for inhibiting said non-zero-frequency indicating pulse train output in response to only a non-zero-frequency component of said sampled video signal of less than a preselected threshold.

11. In a periodically sampled video signalling system, digital means for generating a synthetic video signal in response to a sampled video input having a spectral component within a bandwidth region below the sampling frequency at which said video input is periodically sampled, and comprising pulse train generator means responsive to said sampling frequency for providing a first pulse train;

a first up-down counter responsive to said pulse train for generating a digital output indicative of the integral of the pulse train input thereto and having a control input;

a differential amplifier responsive to the analog amplitude of each of said sampled video input and said digital output of said first counter for providing an up-down control signal to said control input of said first counter;

trigger generator means responsive to said differential amplifier for providing a pulse output in response to each change of sense of said up-down control signal; and

coincidence signalling means responsive to the coincidence of the sample interval of said sampled video input and a preselected state of said pulse output of said trigger generator for generating a synthetic video output.

12. The device of claim 11 in which said coincidence signalling means comprises an output up-down counter having one of an up-count and a down-count input coupled to a source of a reference periodic signal, the other of said inputs being coupled to the output of said trigger generator means;

and a coincidence gate having a first input coupled to said pulse train generator means and a second input coupled to an output of said second up-down counter.

13. The device of claim 12 in which said downcount input of said output counter is coupled to a reference periodic signal source having a variable periodicity.

14. The device of claim 11 in which said coincidence signalling means comprises an up-down counter having an up-count input responsive to the output of said trigger generator means and a down count input responsive to the output of reference periodic signal source having an adjustable periodicity;

and a coincidence gate having a first input coupled to an output of said output counter and a second input responsive to the sampled interval of said sampled video signal for providing a synthetic video output in response to the coincidence of a preselected overflow condition of said second counter and said sampled interval.

15. The device of claim 11 in which said trigger generator includes threshold means for limiting said trigger output response thereof to system sampled video inputs representing a non-zero frequency component video envelope and having at least a preselected threshold amplitude.

16. The device of claim 11 in which said trigger generator means is further responsive to said pulse train generator means and includes threshold means for limiting said pulse output as a response to a preselected number of pulse outputs of said pulse train generator occurring between subsequent changes of sense of said control signal.

17. The device of claim 11 in which said trigger generator comprises a second up-down counter responsive to said control signal output of said differential amplifier and to said pulse train generator means for indicating the integral of each pulse train associated with a change of sense of said control signal;

threshold comparator means coupled to said second counter for inhibiting said counter in response to an output thereof exceeding a preselected threshold; and

monostable signalling means for generating a trigger output in response to said threshold response to said comparator means.

18. In a periodically sampled video signalling system, digital means for generating a synthetic video signal in response to a sampled video input having a spectral component within a bandwidth region below the sampling frequency at which said video input is periodically sampled, and compRising pulse train generator means responsive to said sampling frequency for providing a periodic pulse train;

a first up-down counter responsive to said pulsed train for generating a digital output indicative of the integral of a pulse train input thereto and having an up-down control input;

a differential amplifier responsive to the analog amplitude of each of said sampled video input and said digital output of said first counter for providing an up-down control signal to said control input of said first counter for closed loop control thereof;

trigger generator means responsive to said frequency generator means and said differential amplifier for providing a second pulsed output; and

, coincidence signalling means responsive to the coincidence of said sampled interval of said sampled video and an output of said trigger generator for generating a synthetic video output.

19. Digital doppler processing means for utilization in a spaceborne moving target indicating type of pulsed-energy ranging system, and comprising range gating means responsive to both a video receiver output and a system trigger of said pulsed energy system and having a plurality of range-gated outputs, each representing range-gate sampling of a successive range bin of a receiver range trace signal;

a like plurality of digital filter means as range gated outputs of said range gating means, each said digital filter means comprising a digitizer responsive to a mutually exclusive one of said range gate outputs for providing a pulse train output indicative of a non-zero frequency component of the video envelope of the associated range-gated video output, and coincidence signalling means responsive to the coincidence of the gating interval of said range gate output and a preselected state of the output of said digitizer for generating a synthetic video output; and

signal combining means responsive to said synthetic video outputs of said plurality of digital filter means for providing a doppler-processed AMTI range trace signal.

20. The device of claim 19 in which said coincidance signalling means includes bandpass limiting means comprising a voltage controlled oscillator having a periodicity corresponding to a lower limit frequency of a selected bandpass limit of said filter;

an up-down counter having an up count input coupled to the output of said digitizer and a down count input coupled to an output of said voltage-controlled oscillator; and

a coincidence gate responsive to a preselected output state of said counter and the gating interval of said range gate output for generating a synthetic video output signal.

21. The device of claim 20 in which there is further included a function generator for generating a control voltage indicative of a preselected function for control of said voltage controlled oscillator.

22. The device of claim 20 in which there is further provided means for varying the frequency of said voltage controlled oscillator in accordance with the product of the platform velocity and cosine of the look angle of said pulsed energy ranging system.

23. The device of claim 19 in which said digitizer includes threshold means for limiting the output response thereof to system sampled video inputs representing a non-zero frequency component video envelope having at least a preselected threshold amplitude.