TIME-DOMAIN CORRELATOR FOR SPATIAL FILTERING IN A PULSED ENERGY SYSTEM

• US 3,720,950 A
• Filed: 11/28/1967
• Issued: 03/13/1973
• Est. Priority Date: 11/28/1967
• Status: Expired due to Term

• Current Assignee: Charles L. Vehrs Jr
• Original Assignee: Charles L. Vehrs Jr
• Inventors: Vehrs, Charles L. Jr.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US04/686,113
• Time in Patent Office: 1,932 Days
• Field of Search: 343/17.2PC,17.1,14,5DP,7.7,17.2
• US Class Current: 342/162
• CPC Class Codes: G01S 13/288 phase modulated

Abstract

A pulse compression coded type pulsed energy system having timedomain correlation means permitting narrow-band processing of wide band receiver signals without comprising the data resolution limits thereof. Local oscillator injection means provides a coded periodic sampling signal at a local oscillator input of an intermediate frequency receiver, the sampling periodicity of which sampling signal is substantially less than the system pulse repetition interval and the coding of which sampling signal is a replica of that transmitted by the pulsed energy system. The time-phase of the sampling periodicity of the sampling signal is discretely progressively varied each pulse repetition interval. Data matrix storage means responsive to the variable time-phase sampling signals reconstructs a range trace signal of improved resolution, which may be further processed by radial extent logic to effect spatial filtering within system subpulse intervals.

Claims

1. In a coded pulsed energy system, including an intermediate frequency receiver stage having a local oscillator input, timedomain correlation means comprising local oscillator injection means in cooperation with said intermediate frequency receiver for applying a coded periodic sampling signal at said local oscillator input of said intermediate frequency receiver stage, the sampling periodicity of which sampling signal is substantially less than the pulse repetition interval of said system and the time-phase of which sampling periodicity is discretely progressively varied each pulse repetition interval by an amount less than said sampling periodicity, and the coding of which coded sampling signal is a replica of that transmitted by said pulsed energy system;

and data matrix storage means responsive to said variable time-phase sampled signals for reconstructing a range trace signal having an improved range resolution corresponding to the reciprocal of the transmitted bandwidth.

2. The system of claim 1 in which said data matrix means includes rangegated signal thresholding means and comprises range-gated time averaging means for determining and storing the average signal level of each pulse-compression range-bin of range trace signals sampled by said correlator of said system, and lower limit comparator means responsive to said range trace signals and to said average signal levels for providing a range-bin thresholded range trace signal indicative of a signal return at each range bin in excess of an average signal return at such range bin.

3. The device of claim 2 in which there is further included means responsive to said signal thresholding means for distinguishing targets having at least a minimum radial velocity relative to said system and comprising means for comparing corresponding portions of successive range trace signal histories to determine those unlike corresponding portions indicative of the range-change of a target occurring during the interval between the occurrence of said corresponding portions.

4. The device of claim 2 in which there is further provided spatial filtering means coupled to said signal thresholding means for distinguishing targets having at least a preselected minimum radial velocity relative to said system.

5. The device of claim 2 in which there is further included means for distinguishing targets having at least a preselected minimum radial velocity relative to said system and comprising first and second shift register means, each having an input responsively coupled to said signal thresholding means for providing a respective first and delayed second range trace signal histories;

and nor-gate means having a first and second input respectively coupled to an output of a mutually exclusive one of said shift register means, for providing an output indicative of the non-coincident states of compared portions of said first and delayed second time histories.

6. The device of claim 2 in which said data matrix means further includes upper limit comparator means responsive to said range trace signals and having a reference input responsively coupled to a biased output of said range-gated time averaging means, and logic means responsely coupled to said upper and lower limit comparator means for providing an output indicative of a range-gated range trace signal having an amplitude within preselected upper and lower amplitude limits.

7. The device of claim 1 in which there is a further provided spatial filter means responsive to said data matrix means for indicating the detection of a target having a radial extent within preselected limits.

8. The device of claim 7 in whicH said spatial filter means comprises first logic means for determining the detection of a target having at least a preselected minimum radial extent;

second logic means for determining the absence of a target having a preselected maximum radial extent, and third logic means responsive to said first and second logic means for providing an output signal indicative of the detection of a target of at least said preselected minimum radial extent and less than said preselected maximum radial extent.

9. The device of claim 1 in which said data matrix means comprises two-limit amplitude comparator means for indicating a target return signal for each range-bin and having an amplitude within preselected limits.

10. The device of claim 1 in which said data matrix means comprises two-limit amplitude comparators means for indicating a target return signal from each range-bin and having an amplitude within a preselected upper amplitude limit and above a selected threshold level associated with such range-bin;

and in which there is further provided two-limit spatial filtering means responsive to the output of said two-limit amplitude comparator for indicating whether said amplitude-qualified signal represents a target having a radial extent within a preselected upper and lower radial limit.

11. The device of claim 1 in which said coded pulsed energy system is of the pulse compression type and includes an intermediate frequency receiver stage having a receiver-mixer in cooperation with a stable local oscillator for providing a source of frequency fs, and in which said local oscillator injection means comprises an intermediate frequency oscillator as a source of frequency fIF;

filtered mixing means responsive to the coded spectra (fT) utilized by a transmitter of said pulse compression system and further responsive to said sources of frequency fs and fIF for providing a local oscillator injection signal spectrum (fT -(fs + fIF)); and

first receiver mixing means responsive to a pulse-compressed output of a receiver of said pulse compression system and having a local oscillator input responsive to said local oscillator injection signal for providing a lower sideband frequency translated output (fs + fIF) to an input of said receiver-mixer of said intermediate frequency receiver stage.

12. The device of claim 11 in which there is further provided radio-frequency conditioning means in cooperation with said stable local oscillator for converting received echoes of the radio frequency spectrum (fT) transmitted by said pulsed energy system to a conjugate side band of the transmitted spectrum.

13. The device of claim 11 in which there is further provided switchable dispersive delay means having a transmit and receive switching modes, said delay means input-coupling a source of said coded spectrum fT to a transmitter of said pulsed energy system during said transmit-switching mode to provide frequency modulation of a pulsed transmission;

and radio-frequency conditioning means in cooperation with said stable local oscillator for converting received echoes of the transmitted radio frequency spectrum (fT) to a conjugate sideband of the transmitted spectrum, said delay means being interposed between an output of said radio frequency conditioning means and an input of said first receiver mixing means during said receive switching mode for providing a pulse compressed receiver input to said first receiver mixing means.

14. In a pulse-compression type pulsed energy system having a receiver, data processing means comprising two-limit amplitude comparator means responsively-coupled to said receiver for providing an output indicative of a rangegated target return signal from each of successive range bins and having an amplitude within a preselected upper amplitude limit and above a selected threshold level associated with such range bin;

and two-limit spatial filtering means responsive to the output of said two limit amplitude comparator for indicating whether said amplitude-qualified signal represents a target having a radial extent within a preselected upper and lower radial limit.

15. The device of claim 14 in which said two-limit spatial filter comprises first radial extent signalling means responsive to said two-limit amplitude comparator for providing an output indicative of the presence of an amplitude-qualified target signal corresponding to at least a preselected minimum target radial extent;

second radial extent signalling means responsive to said two-limit amplitude comparator for providing an output indicative of the absence of an amplitude qualified target signal corresponding to at least a preselected maximum radial extent; and

logic means responsive to said first and second radial extent signalling means for providing an output indicative of an amplitude qualified target signal representing a target having a radial extent within said two preselected radial extent limits.

16. The device of claim 14 in which said two-limit spatial filter comprises an input terminal;

first and second coincident logic signalling means;

first tapped delay line means having an input coupled to said input terminal and further having a plurality of successive taps coupled to said first coincident logic signalling means, the interval between adjacent taps corresponding to a sampled range bin and the plurality of taps corresponding to a preselected minimum radial extent;

second tapped delay line means having an input coupled to said input terminal and further having a plurality of successive taps coupled to said second logic signalling means, the interval between adjacent taps corresponding to a sampled range bin and the plurality of taps corresponding to a preselected maximum radial extent; and

third logic means responsive to a first state of said first logic means and to a second state of said second logic means for indicating an input signal on said input terminal having a duration corresponding to a radial extent greater than said minimum radial extent and less than said maximum radial extent.

17. The device of claim 14 in which said two-limit spatial filter comprises an input terminal;

first and second coincident logic signalling means;

tapped delay line means having an input terminal and further having a first and second plurality of successive taps respectively coupled to said first and second coincident logic signalling means, the interval between adjacent taps corresponding to a sampled range bin and the first plurality of taps corresponding to a preselected minimum radial extent, said second plurality of successive taps including said first plurality and corresponding to a preselected maximum radial extent; and

third logic means responsive to a first state of said first logic means and to a second state of said second logic means for indicating an input signal on said input terminal having a duration corresponding to a radial extent greater than said minimum radial extent and less than said maximum radial extent.

18. In a frequency-modulation type pulse compression system, narrow bandwidth intermediate frequency correlation means for processing wide bandwidth data without compromising the data resolution limits thereof and comprising an intermediate frequency receiver stage including a mixer having a first input responsive to received echoes of frequency-modulated pulsed energy transmitted by said system, and further having a second local oscillator input;

a periodically frequency-modulated local oscillator for providing during each system pulse repetition interval a pulse train of frequency-modulated pulses of like pulsewidth as said transmitted energy, the frequency modulation of said pulse train differing from that of said transmitted energy by an amount correspOnding to a preselected intermediate frequency, said second input of said mixer being coupled to an output of said local oscillator;

periodic programmer means for cyclically, discretely, progressively adjusting the time phase of said local oscillator pulse train, relative to the occurrence of said transmitted energy, each system pulse repetition interval, said programmer having a periodicity of n system pulse repetition intervals; and

data matrix storage means responsive to said programmer and to said intermediate frequency receiver stage for providing a range trace data matrix of in range-gated data-elements corresponding to contiguous range bins.

19. In a frequency-modulation type pulse compression system, narrow bandwidth intermediate frequency correlation means for processing wideband width data without compromising the data resolution limits thereof and comprising an intermediate frequency receiver stage including means providing a periodically frequency-modulated local oscillator input each pulse repetition interval, said local oscillator input comprising a pulse train of i frequency-modulated pulses of like pulsewidth as said transmitted energy, the frequency modulation of said pulse train differing from that of said transmitted energy by an amount corresponding to a preselected intermediate frequency, periodic programmer means for cyclically discretely, progressively adjusting the time phase of said local oscillator pulse train, relative to the occurrence of said transmitted energy, each pulse repetition interval, said programmer having a periodicity of n pulse repetition intervals;

and data matrix storage means responsive to said programmer and to said intermediate frequency receiver stage for providing a range race data matrix of in range-gated data elements, corresponding to contiguous range bins.

20. In a pulsed energy system including a frequency-modulated transmitter and an intermediate frequency receiver stage responsive to received echoes of pulsed energy transmitted by said transmitter and having a local oscillator input, narrow bandwidth correlation means for processing wide bandwidth data without compromising the data resolution limits thereof, and comprising local oscillator injection means cooperating with said intermediate frequency receiver stage for periodically sampling a received signal during each pulse repetition interval to provide a range-bin sampled range trace signal;

and means for adjusting the time-phase of said periodic sampling for increasing the number of range-bins sampled over a preselected data processing interval.

21. The device of claim 20 in which said intermediate frequency receiver stage includes a plurality of intermediate frequency receivers commonly responsive to said received echoes, each receiver having a separate local oscillator input;

and which said local oscillator injection means comprises a like plurality of local oscillators as intermediate frequency receivers, each local oscillator cooperating with a mutually exclusive one of said receivers for sampling a mutually exclusive set of range-bins.

22. The device of claim 20 in which there is further provided data matrix storage means responsive to said intermediate frequency receiver and said means for adjusting for reconstructing a range trace signal of improved resolution from said range-bin signal samples.

23. In a frequency modulated pulsed energy system, including an intermediate frequency receiver stage having a local oscillator input, time-domain correlation means comprising local oscillator injection means in cooperation with said intermediate frequency receiver for applying a periodic sampling signal at said local oscillator input of said intermediate frequency receiver stage, the sampling periodicity of which sampling signal is an integer submultiple of the pulse repetition interval of said system and the time-phase of which sampling periodicity is discretely progressively varied each pulse repetition intervaL by a submultiple of said sampling periodicity;

and data matrix storage means responsive to said variable time-phase sampled signals for reconstructing a range trace signal having an improved range resolution corresponding to the reciprocal of the transmitted frequency-modulation bandwidth, BW.

24. A frequency modulated pulse compression type pulsed energy system including an intermediate frequency receiver stage having a receiver-mixer in cooperation with a stable local oscillator for providing a source of frequency fs, and comprising an intermediate frequency oscillator as a source of frequency fIF;

filtered mixing means responsive to the coding spectra (fT) utilized by a transmitter of said pulse compression system and further responsive to said sources of frequency fs and fIF for providing a local oscillator injection signal spectrum (fT -(fs + fIF));

first receiver mixing means responsive to a pulse-compressed output of a receiver of said pulse compression system and having a local oscillator input responsive to said local oscillator injection signal for providing a lower sideband frequency translated output (fs - fIF) to an input of said receiver-mixer of said intermediate frequency receiver stage;

switchable dispersive delay means having a transmit and receive switching modes, said delay means input-coupling a source of said coding spectrum fT to a transmitter of said pulsed energy system during said transmit-switching mode to provide frequency modulation of a pulsed transmission; and

radio-frequency conditioning means in cooperation with said stable local oscillator for converting received echoes of the transmitted radio frequency spectrum (fT) to a conjugate sideband thereof, said delay means being interposed between an output of said radio frequency conditioning means and an input of said first receiver mixing means during said receive switching mode for providing a pulse compressed receiver input to said first receiver mixing means.

25. In a pulse compression type system providing a thresholded high-resolution signal output, means responsive to said signal output for providing a first and a delayed second range trace signal, and means responsive to said first and said delayed second range trace signal for providing a third range trace signal indicative of detected moving targets.

26. The device of claim 25 in which the output of said second mentioned means is indicative of moving targets having velocities within a selected upper and lower velocity limit.