MEANS AND METHOD FOR DETECTING DOPPLER SIGNALS SUBMERGED IN CLUTTER

• US 3,603,996 A
• Filed: 08/09/1968
• Issued: 09/07/1971
• Est. Priority Date: 08/09/1968
• Status: Expired due to Term

• Current Assignee: Alexander G. Antonio, Jerre M. Murchison
• Original Assignee: Alexander G. Antonio, Jerre M. Murchison
• Inventors: Murchison, Jerre M., Antonio, Alexander G.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US04/752,733
• Time in Patent Office: 1,124 Days
• Field of Search: 343/7.7,9
• US Class Current: 342/28
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242

Abstract

A subclutter, personnel detection coherent pulsed doppler radar system for discerning doppler signals submerged in clutter incorporating range gating, clutter rejection and clutter cancellation for use in a highly foliated environment, the received returns gated to eliminate all but those from the surveillance bin at a preselected range, the antenna pattern shaping the resolution cell in both azimuth and elevation. A filter system limits undesired received signals, the passed signal being separated into separate channels for receding or approaching targets, the outputs of the channels being subtracted and then integrated. Since foliage movement is fixed but pliable, the received clutter signal therefrom will integrate to zero voltage level, while with signals received from a target exhibiting continuous radial motion, the doppler signal will integrate to a level which may be displayed or recorded.

Claims

1. A system for detecting doppler signals submerged in clutter, comprising:

A. means generating energy;

B. means transmitting energy;

C. means receiving echo energy from approaching and receding targets containing doppler information;

D. means simultaneously processing the doppler spectrum from the approaching and receding targets contained in the received echo energy to produce a signal proportional to net target motion.

2. a timer means comprising a pulse repetition frequency generator and a range gate generator providing the timing pulse for a range gate in said receiver means;

and

3. The system defined by claim 2 wherein said cancelling means comprises:

A. means separating the upper and lower sidebands of the doppler spectrum;

B. means operative to cause the separated sidebands to be detected and integrated and operative to readout any resultant signal.

4. a boxcar generator operative to stretch the video signal in time to cover substantially the entire pulse repetition period;

D. said processing means comprises;

5. The system defined by claim 4 wherein said means separating the sidebands of the doppler spectrum are controlled by said clock means to maintain the center frequency of said sideband separating means an absolute value on either side of a reference frequency, and said detection and integration means includes means which indicates if the summation over the integration period is not zero.

6. The system defined by claim 4 wherein said means separating the sidebands of the doppler spectrum are controlled by said clock means, means velocity weighting each sideband and said detection and integration means includes means integrating the velocity weighted sideband Spectrum with respect to time so that the output is proportional to the summation of the cross section of all targets and their displacement.

7. The device defined by claim 1 wherein:

A. said generating means produces pulsed, coherent RF energy and comprises;

8. The detection device defined by claim 7 wherein:

A. said canceler means comprises;

9. The detection device defined by claim 7 wherein:

said canceler means comprises;

A. plural narrow band-pass digital filters for receiving the signal passed by said doppler spectrum filter means dependent on the relative magnitude of the passed signal;

the center frequency of the said digital filters controlled and established by said clock means;

B. detector and integrator means for each said digital filter detecting and integrating the outputs of said digital filters;

C. a summation amplifier summing the signal output of said detector and integration means; and

D. readout means responsive to any signal from said summation amplifier which is larger, in either sEnse, than a preselected value.

10. In a system detecting amplitude and frequency of a returned signal containing doppler information, the means for cancelling signal information resulting from fixed but pliable movement while retaining that resultant from continuous radial motion, comprising:

A. means separating the sidebands of the returned doppler information containing signal;

B. means detecting and integrating the separated sidebands to produce a signal proportional to net target motion;

C. clock means establishing and controlling the center frequency of said sideband separating means to maintain the center frequency of said sideband separating means an absolute value on either side of the center frequency.

11. The means defined by claim 10 including a filter means having a filter center frequency established and controlled by said clock means rejecting stationary target return signals.

12. The method of detecting in a target area an object having continuous radial motion which is obscured by objects exhibiting fixed but pliable movement comprising:

A. detecting the amplitude and frequency of a returned signal containing doppler information from the target area;

B. separating the sidebands of the detected return signal by establishing a center reference frequency so that the sidebands represent a function of the amplitude of all targets exhibiting motion versus frequency;

C. velocity weighting the doppler spectrum in each separated sideband;

D. integrating the spectrum with respect to time to obtain a signal which is proportional to the summation of the cross section and displacement of all target signals exhibiting a doppler shift so that the summation of the two sidebands will cancel to a predictable level over the integration period where objects in the target area are fixed but pliable but where objects exhibit continuous radial motion the signal return will add only to one of the sidebands.

13. The method defined by claim 12, including the additional step prior to separating the sidebands of filtering the returned signal to remove any signal not exhibiting a doppler shift.