Radar and IFF system

• US 6,420,995 B1
• Filed: 04/05/1965
• Issued: 07/16/2002
• Est. Priority Date: 04/05/1965
• Status: Expired due to Term

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: Systems Information and Electronic Systems Integration Incorporated
• Inventors: Richmond, Martin R., Goulder, Morton E.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US04/446,144
• Time in Patent Office: 13,616 Days
• Field of Search: 343/100, 343/7, 343/5, 343/17.1, 343/11, 343/13, 343/14, 343/17.2, 342/13, 342/16, 342/17, 342/18, 342/19, 342/20, 342/82, 342/83, 342/85, 342/88, 342/89, 342/91, 342/94, 342/198
• US Class Current: 342/45
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures

Abstract

A silent radar system which detects a target and its position without the countermeasure operator located at the target being able to detect the presence of the radar. The silent radar operates by transmitting signals with specific characteristics which allow optimum processing by the radar while taking advantage of the limitations inherent in typical signal receiving equipment. The silent radar transmits low energy per cycle signals which are wideband, purely random noise, e.g. spread spectrum signals.

Claims

1. A silent operating radar system having a controllable silent range, within which range another receiver system having set operating characteristics cannot detect the presence of said silent operating radar system, comprising:

A. means for providing optimized radar signal reception of a magnitude greater than said other receiver system,

B. means for producing a controlled signal energy spread over a wide bandwidth to thereby establish a low value of energy at any specific single frequency in said bandwidth, said low value, of energy per specific single frequency being less than a level at which said other receiver system with its set operating characteristics can detect while in said silent range, whereby said silent operating radar system is thus afforded a detection advantage over said other radar system because of the combined presence of said optimized radar reception and of said low controlled value of energy per specific single frequency.

2. The system described in claim 1 where said means for providing a controlled signal energy produces signal energy per single frequency that will not be detectable to said receiver system because the inherent path loss between said silent radar system and said receiver system will place said signal below the level of detectability of said receiver system'"'"'s set characteristics within said silent range.

3. The system described in claim 1, including control means to vary the signal power output to thereby control the distance of said silent range.

4. The system described in claim 3 wherein said control means are controlled by the location of said receiver system in said silent range.

5. The system described in claim 3 wherein said control means has a controlled programmed input to thereby control the silent range covered in a predetermined manner.

6. A silent operating radar system having a self-protection shell, said shell being defined as the volume between two hemispherical shells where said silent operating radar is located at a common center of radii that would be included in both of said shells, said self-protection shell acting as a protector of said silent operating radar when another radar system having set operating characteristics is within said volume defined by said shell, said volume being a function of the output power of said silent operating radar, said silent operating radar comprising:

A. means for providing an optimized radar signal reception capability of a magnitude greater than said other radar system,

B. means for producing signal energy spread over a wide bandwidth to thereby establish a low value of energy at any specific single frequency in said bandwidth, said low value of energy per specific single frequency being less than a level at which said other system with its set operating characteristics can detect while anywhere in the volume defined as said self-protection shell, whereby said silent operating radar system is thereby afforded a detection advantage over said other radar system because of the combined presence of said optimized radar reception and of said low value of energy per specific single frequency.

7. The system described in claim 6, including control means to vary the signal power output of said silent operating radar system to thereby alter the volume of said self-protection shell, said control means thereby acting to control the dimensions of said self-protection shell to effectively vary the range within which said self-protection shell will afford silent range operation of said system when said other radar with said set operating characteristics is within the volume defined by said self-protection shell.

8. A silent operating radar system in which the power output of said radar is in part controlled by the position of a target in space, comprising:

A. means for transmitting a signal having a controlled power level such that attenuation of said power output to said target is at a level not discernible by a receiver in said target;

B. means for detecting a target reflected portion of the transmitted signal, such that there is provided a silent operating radar system.

9. The radar system of claim 8 including means for programming said controlled power output level to always maintain said power output level below said level of discernibility in said target receivers.

10. A silent operating radar system in which the power output of said radar is in part controlled by the position of a plurality of targets in space, comprising:

A. means for transmitting a signal having a controlled power level such that attentuation of said output to each of said targets is at a level not discernible by a receiver in said targets;

B. means for detecting a target reflected portion of the transmitted signal, such that there is provided a silent operating radar system.

11. The radar system of claim 10, including means for programming said controlled output level to always maintain said power output level below said level of discernibility in each of said target'"'"'s receivers.

12. A silent operating radar system in which the power output is of wide band random noise and said radar'"'"'s power output is in part controlled by the position of a target in space, comprising:

A. means for transmitting a signal of wide band random noise characteristic having a controlled power level such that attenuation due to travel through space by said wide band random noise power output to said target results in said signal not being discernible by a receiver in said target;

B. means for detecting a target reflected portion of the wide band random noise transmitted signal, such that there is provided a silent operating radar system.

13. The radar system of claim 12, including means for programming said controlled wide band random noise power output level to always maintain said power output level below said level of discernibility in said target.

14. The radar system of claim 12 which includes means whereby said power level is controlled by a plurality of targets.

15. The radar system of claim 14 wherein said controlled wide band random noise power output level is programmed to always maintain said power output level below said level of discernibility in each of said target receivers.

16. A closed loop silent radar system having a controlled power output, wherein a target becomes part of the closed loop, said radar system comprising

A. transmitter means having a controlled output for sending a signal to said target,

B. memory means to store information with reference to said target'"'"'s range and azimuth,

C. a range receiver means receiving a reflected signal from said target and having an output signal fed to said memory means,

D. an azimuth position means for controlling scanning having an output signal indicative of its position fed to said memory means,

E. said memory means simultaneously receiving both said range receiver means output signal and said azimuth position output signal to produce a controlled signal to said transmitter means to thereby provide a controlled power output which power output is of an optimum level such that the target can be detected but said target cannot detect the presence of said radar system'"'"'s transmitter means output.

17. The radar system of claim 16 wherein said transmitter includes means for producing a controlled power output of wide band purely random noise.

18. The radar system of claim 16 wherein said memory means output controls said transmitter means to automatically set the transmitted output power at said optimum level for individual targets at different range-azimuth coordinates.

19. The radar system of claim 18 wherein said azimuth signal stored in said memory means will control said transmitter power means to shift the output power to a different level at azimuth positions that have no target.

20. The radar system of claim 16 wherein said range receiver means utilizes cross-correlation to compare a target reflected signal with a known delayed signal to establish the range of said target.

21. The radar system of claim 16 wherein said memory means record continuously the azimuth and range history of said target to thereby provide a continuously controlled output from said transmitter means.

22. The combination set forth in claim 16 and further including means to sample power level in said transmitter means,

A. comparison means to compare said sampled power level with a fixed level, said comparison means producing an error signal proportional to the difference between said sampled power output and said fixed level,

B. whereby said error signal will control output power to regulate said power output.

23. The combination set forth in claim 22 wherein there is included means to control said reference level as a function of said memory output power control means.

24. The power regulation system of claim 23 wherein said transmitter means controlled power output is of wide band purely random noise.

25. The power regulation system of claim 23 wherein said memory means causes said transmitter means to automatically set power at said optimum level for individual targets at different range-azimuth coordinates.

26. The power regulation system of claim 25 wherein said azimuth position means output signal to said memory means will control said transmitter power output to shift to a different level at azimuth positions that have no target.

27. A silent radar system to detect a target that has radar reception capabilities comprising a clock pulse generator means to provide a train of pulses and a noise generating means to provide a noise signal,

A. a coincidence gate means receiving both said train of pulses and said noise signal, said coincidence gate means having a resulting output random noise pulse train signal,

B. a continuous wave oscillator means,

C. a modulator means being fed a continuous wave oscillator signal input from said continuous wave oscillator means and a random noise pulse train signal input from said coincidence gate,

D. said modulator means controlling said continuous wave signal input and said random noise pulse train signal to provide a random phase shifted signal output,

E. a variable attenuator means being supplied said random phase shifted signal and controlled by a program means to maintain a system power output that will always be undiscernible to said target with radar reception capabilities,

F. transmitter means fed by said variable attenuator means for directing said random phase shifted signal output signal toward said target,

G. receiver means for receiving a reflected portion of said output signal from said target carrying doppler information as to said target'"'"'s velocity and having an output fed to a coherent mixer which mixer has simultaneously fed thereto a continuous wave oscillator signal from said continuous wave oscillator means,

H. time delay means being fed a portion of said random noise pulse train from said coincidence gate means,

I. said time delay means having stored therein said random noise pulse train history from said coincidence gate means,

J. said time delay means having a plurality predetermined time delay taps each representing a different time equivalent to the time a signal from said attenuator output takes to reach said target and be reflected back to said receiving means,

K. a plurality of correlation mixers equivalent in number to said time delay taps each being fed simultaneously by said coherent mixers output and one of said time delay taps whereby a correlation output signal will occur only in a correlation mixer that has a random noise pulse train signal that matches said reflected signal with an equivalent time delay,

L. said correlation output signal thereby providing an indication of said target and its range.

28. The silent radar system of claim 27 wherein each of said correlation mixers have an output fed to a doppler filter bank means, said doppler filter bank means functioning to extract radial velocity information from said correlation output signal.

29. The silent radar system of claim 27 in combination with

A. a memory means to store information with reference to said target'"'"'s range and azimuth,

B. said correlation output signal with its target range information being fed to said memory means,

C. an azimuth position means for controlled scanning having an output signal indicative of its position fed to said memory means,

D. said memory means simultaneously receiving both said correlation output signal with its target range information and said azimuth position output signal to vary said attenuator means to thereby provide a controlled power output of an optimum level such that said target cannot detect the presence of said silent radar system output which has been directed toward said target.

30. The silent radar system of claim 29 wherein said memory means output controls said transmitter means to automatically set power at said optimum level for individual targets at different range-azimuth coordinates.

31. The silent radar system of claim 30 wherein said azimuth position means output signal to said memory means will control said attenuator means power output to shift to a different level at azimuth positions that have no target.

32. The silent radar system of claim 27 having said attenuator output fed to a frequency dispersive network prior to being fed to said transmitter means thereby allowing the transmission of wide band noise signals not readily discernible by said target aircraft.

33. The silent radar system of claim 32 wherein said receiver means has a spectrum compressing means to thereby reconstitute the frequency dispersion that occurred in said frequency dispersive network and provide a signal which is more readily processed.

34. The combination of claim 28 wherein said doppler filter band means consists of narrow band filters whose characteristics have been selected to achieve unambiguous range and velocity information.

35. The combination of claim 27 wherein said delay means consists of a continuously variable delay device.

36. Silent radar system for locating a target carrying a receiver without being detected by said receiver comprising

A. means for transmitting wide band random noise signals,

B. means for storing the history of said signals prior to transmissions,

C. means for receiving said transmitted signals reflected from said target,

D. means for comparing said reflected signals with said stored signals,

E. means for deriving from said compared signals information as to the target'"'"'s position and velocity,

F. and means for controlling the signal level of said transmitted signals so that said transmitted signals cannot be detected at said target'"'"'s receiver means, while the received signals at said radar receiver means reflected from said target can be detected.

37. Silent radar system for locating a target carrying a receiver without being detected by said receiver comprising

A. means for transmitting wide band signals,

B. means for storing the history of said signals prior to transmission,

C. means for receiving said transmitted signals reflected from said target,

D. means for comparing said reflected signals with said stored signals,

E. means for deriving from said compared signals information as to the target'"'"'s position and velocity,

F. and means for controlling the power level of said transmitted signals so that said transmitted signals cannot be detected at said target receiver while the received signals at said radar receiver means reflected from said target can be detected.

38. The combination of claim 37 wherein said means for controlling the signal level of said transmitted signals contains programming means to always maintain said transmitted signal level below the limit of discernibility of said receiver in said target.

39. The combination of claim 37 wherein said control means further includes means for controlling the signal level of the transmitter signal for a multiplicity of targets having different range-azimuth coordinates.

40. The combination of claim 39 wherein said transmitting means further includes sector scan means for controlled scanning in a preselected pattern.

41. Silent radar system for locating a target carrying a receiver without being detected by said receiver comprising

A. means for transmitting a spectrum of noise signals,

B. means for storing the history of said signals prior to transmission,

C. means for receiving said transmitted signals reflected from said target,

D. means for comparing said reflected signals with said stored signals,

E. means for deriving from said compared signals information as to the target'"'"'s position and velocity,

F. and means for controlling the signal level of said transmitted signals so that said transmitted signals cannot be detected at said target receiver means while the received signals at said radar receiver means reflected from said target can be detected.

42. The combination of claim 41 wherein said means for controlling the signal level of said transmitted signal includes

A. a memory logic unit containing a stored program fed from said range information means,

B. a range power function generator fed from said memory logic unit,

C. and a variable attenuator controlled by said range power function generator to set the signal level of said transmitted signals.

43. Silent radar system for locating a target carrying a receiver without being detected by said receiver comprising

A. means for transmitting pseudo random noise signals,

B. means for storing the history of said signals prior to transmission,

C. means for receiving said transmitted signals reflected from said target,

D. means for comparing said reflected signals with said stored signals,

E. means for deriving from said compared signals information as to the target'"'"'s position and velocity,

F. and means for controlling the signal level of said transmitted signals so that said transmitted signals cannot be detected at said target receiver means while the received signals at said radar receiver means reflected from said target can be detected.

44. An IFF and silent radar system for detection and identification of friendly targets at a distance without said target being able to determine it was detected and interrogated comprising

A. receiver means carried by said target,

B. electronic jammer means of the repeater type carried by said target operating in conjunction with said receiver means for transmitting signals in a predetermined manner,

C. means at said radar for transmitting wide band random noise signals,

D. means at said radar for storing the history of said signals prior to transmission,

E. said receiver means at said target receiving said transmitted signals and said jammer means transmitting said signals in a predetermined pattern,

F. means at said radar for receiving said transmitted signals reflected from said target and from said jammer,

G. means at said radar for comparing said reflected and said jammer signals with said stored signals,

H. means at said radar for deriving from said compared signals information as to the target'"'"'s position and velocity,

I. means at said radar for deriving from said compared signals information as to the target'"'"'s identity,

J. and means for maintaining the signal level of said radar transmitted signals so that said transmitted signals cannot be detected at said target'"'"'s receiver means, while the received signals at said radar receiver means reflected from said target transmitted by said jammer can be detected.

45. A system for identifying a friendly target at a distance without said target being able to determine it was detected and identified comprising

A. receiver means carried by said target,

B. electronic jammer means of the repeater type carried by said target operating in conjunction with said target receiver means for transmitting signals in a predetermined manner,

C. means located at a station remote from said target for transmitting wide band random noise signals,

D. means located at said station for storing the history of said wide band signals prior to transmission,

E. said receiver means at said target receiving said wide band transmitted signals and said jamming means transmitting said signals in a predetermined manner,

F. means located at said station for receiving said signals transmitted by said jammer means,

G. means at said station for comparing said signals from said jammer and said stored signals,

H. means at said station for deriving from said compared signals information as to said target'"'"'s identity,

I. and means for maintaining the signal level of said station'"'"'s wide band transmitted signals at a level that cannot be detected at said target'"'"'s receiver while the received signals can be detected by said station'"'"'s receiver.

46. The method of operating a radar system which can detect a target having an intercept receiver but which cannot be detected by said target which comprises the following steps

A. providing a radar system which is optimized to receive signals not discernible to said target intercept receiver,

B. transmitting a wide band random signal,

C. storing the history of said signal before transmission,

D. receiving said signal reflected from said target,

E. Comparing said received reflected signal with said stored signal,

F. Deriving information from said compared signals as to the target'"'"'s position and speed,

G. and controlling the transmitted signal level so that it cannot be detected by said target receiver while it can be detected by said radar receiver.

47. The method of operating a radar utilizing wide band noise transmission and sensitive signal processing capabilities so that the radar can detect targets having intercept receivers without being discerned by said target which consists of

A. illuminating said target with wide band noise signals,

B. adjusting the power level of said signals so that said target cannot discern them while the reflected signals from said target are discernible to said radar.

48. The method of operating a radar which has a greater sensitivity than the intercept receiver of a target so it detects said target without said target being able to discern it has been detected which consists of

A. illuminating the target with a signal whose level is below the discernible level of said target receiver while the signals reflected from said target are detectable by said radar, and

B. controlling the level of said signals as the target'"'"'s range changes to maintain the signal level undiscernible to the target receiver while still discernible to said radar.