Acquisition system for continuous-wave frequency modulation object detector

• US 4,200,871 A
• Filed: 05/15/1978
• Issued: 04/29/1980
• Est. Priority Date: 06/29/1977
• Status: Expired due to Term

• Current Assignee: SP-Microwave, Inc.
• Original Assignee: Sperry Corporation (Unisys Corporation)
• Inventors: Roeder, Robert S., Bomar, Lucien C. II
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/906,291
• Time in Patent Office: 715 Days
• Field of Search: 343/7.4, 343/7.5, 343/5 R, 343/759, 343/14, 343/757
• US Class Current: 342/78
• CPC Class Codes: G01S 13/341 wherein the rate of change of the transmitted frequency is adjusted to give a beat of predetermined constant frequency, e.g. by adjusting the amplitude or frequency of the frequency-modulating signal
• CPC Class Codes: G01S 13/586 using, or combined with, frequency tracking means

Abstract

A continuous-wave frequency-modulation active radiometric target seeking device performs search, acquisition, and tracking functions. A technique is provided for target range discrimination and recognition using a pair of narrow band i.f. filters also improving both signal-to-clutter ratio and signal-to-receiver noise ratio. Target search is accomplished with simultaneous and synchronized range and antenna azimuth scanning with range bins effectively swept across the target by variably modulating the transmitted carrier frequency. Recognition of a substantially point target is achieved by a bipolar pulse discriminator responsive to the i.f. filter pair. Upon target acquisition, tracking is maintained by imposing a high frequency dither upon the modulation frequency in a closed loop control using only a single i.f. filter.

Claims

1. In a high frequency target detector system having antenna means for conically scanning about a boresight direction and coupled to receiver means:

transmitter carrier oscillator means coupled to said antenna means and to said receiver means,

master oscillator means,

drive means responsive to said master oscillator means for conically scanning said antenna means at a first rate,

sweep generator means responsive to said master oscillator means for frequency modulating said transmitter carrier at a second rate,

azimuth motive means responsive to said master oscillator means for cylically sector scanning said antenna means in azimuth at a third rate,

said sweep generator means, said azimuth motive means, and said conical scanning of said antenna means being operated in synchronous relation, and

utilization means coupled to the output of said receiver means.

2. Apparatus as described in claim 1 additionally including:

target acquisition signal processor means responsive to said receiver means, and

target detector means responsive to said target acquisition signal processor means.

3. Apparatus as described in claim 2 wherein said target acquisition signal processor means includes at least:

first and second narrow band filter means responsive to said receiver means and having substantially contiguous pass bands;

first and second detector means respectively responsive to said first and second narrow band filter means, and

difference amplifier means responsive to said first and second detector means in the presence of a desired target by producing an output having a first polarity portion immediately followed by an opposite polarity portion.

4. Apparatus as described in claim 3 wherein said first polarity portion and said opposite polarity portion are of substantially equal time duration.

5. Apparatus as described in claim 3 wherein said target acquisition signal processor means additionally includes;

first pulse detector means responsive to said first polarity portion,

delay means responsive to said first pulse detector means,

second pulse detector means responsive to said second polarity means, and

gate means responsive to the simultaneous presence of outputs from said delay means and from said second pulse detector means by generation of a coincidence signal,

said target detector means being responsive to said gate means coincidence signal whereby target acquisition is initiated.

6. Apparatus as described in claim 5 wherein:

first frequency divider means responsive to said master oscillator means determines said first rate,

second frequency divider means responsive to said first frequency divider means determines said second rate, and

third frequency divider means responsive to said second frequency divider means determines said third rate.

7. Apparatus as decribed in claim 5 additionally including:

third narrow band filter means responsive to said receiver means and having a pass band contiguous with the pass band of said second narrow band filter means and opposite the pass band of said first narrow band filter means,

third detector means responsive to said third narrow band filter means,

target range tracking means responsive to said third detector means, and

switch means responsive to said target detector means for disconnecting the output of said sweep generator means from said transmitter carrier oscillator means,

said switch means including means for connecting the output of said target range tracking means to control the frequency of said transmitter carrier oscillator means.

8. Apparatus as described in claim 7 wherein said target range tracking means includes:

synchronous detector means responsive to said third detector means, and

integrator means responsive to said synchronous detector means.

9. Apparatus as described in claim 8 additionally including:

dither oscillator means responsive directly to said master oscillator means, and

summation means for adding the outputs of said integrator means and said dither oscillator means from control of the frequency of said transmitter carrier oscillator means.

10. Apparatus as described in claim 5 additionally including:

third narrow band filter means responsive to said receiver means and having a pass band contiguous with the pass band of said second narrow band filter means and opposite the pass band of said first narrow band filter means,

third detector means responsive to said third narrow band filter means,

elevation and azimuth angle error detector means selectively responsive to said third detector means,

first switch means responsive to said target detector means for discontinuing said cyclic sector scanning of said antenna means in azimuth, and

second switch means also responsive to said target detector means for coupling the output of said third detector means to said elevation and azimuth error angle detector means for automatic tracking by said antenna means of said target in azimuth and elevation.

11. Apparatus as described in claim 10 wherein the band widths of said first, second, and third narrow band filter means are substantially equal.

12. Apparatus as described in claim 10 further including quadrature phase reference generator means driven in synchronism by said drive means for furnishing quadrature conical scan reference voltages to said respective elevation and azimuth angle error detector means.

13. In a high frequency target detector system having antenna means for conically scanning about a boresight direction and coupled to receiver means:

transmitter carrier oscillator means coupled to said antenna means and to said receiver means,

master oscillator means,

drive means responsive to said master oscillator means for conically scanning said antenna means at a first rate,

sweep generator means responsive to said master oscillator means for frequency modulating said transmitter carrier at a second rate,

azimuth motive means responsive to said master oscillator means for cyclically sector scanning said antenna means in azimuth at a third rate,

said sweep generator means, said azimuth motive means, and said conical scanning of said antenna means being operated in synchronous relation,

target acquisition signal processor means responsive to said receiver means, and

target detector means responsive to said target acquisition signal processor means,

said target acquisition signal processor including at least;

first and second narrow band filter means responsive to said receiver means and having substantially contiguous pass bands;

first and second detector means respectively responsive to said first and second narrow band filter means, and

difference amplifier means responsive to said first and second detector means in the presence of a desired target by producing an output having a first polarity portion immediately followed by an opposite polarity portion,

first pulse detector means responsive to said first polarity portion,

delay means responsive to said first pulse detector means,

second pulse detector means responsive to said second polarity means, and

gate means responsive to the simultaneous presence of outputs from said delay mmeans and from said second pulse detector means by generation of a coincidence signal, and

said target detector means being responsive to said gate means coincidence signal whereby target acquisition is initiated,

said target acquisition signal processor additionally including;

third narrow band filter means responsive to said receiver means and having a pass band contiguous with the pass band of said second narrow band filter means and opposite the pass band of said first narrow band filter means,

third detector means responsive to said third narrow band filter means, and

control means responsive to said third detector means for controlling the gain of at least a portion of said receiver means in the presence of an output from said third detector means.