ADAPTIVE PROXIMITY INDICATING SYSTEM

• US 3,875,570 A
• Filed: 03/27/1973
• Issued: 04/01/1975
• Est. Priority Date: 03/27/1973
• Status: Expired due to Term

• Current Assignee: George B. Litchford
• Original Assignee: George B. Litchford
• Inventors: Litchford, George B.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/345,432
• Time in Patent Office: 735 Days
• Field of Search: 343/6.5R,6.5LC,112CA
• US Class Current: 342/32
• CPC Class Codes: G01S 13/781 Secondary Surveillance Radar [SSR] in general
• CPC Class Codes: G01S 13/933 of aircraft or spacecraft

Abstract

An adaptive proximity indication system using the signals emitted by the hundreds of existing secondary radar ground stations and the nearly 100,000 cooperating transponders on mobile vehicles to detect intrusion in a monitored proximity volume. The system automatically adapts to a given SSR environment to vary the size and shape of the monitored volume and to control its method of proximity measurements.

Claims

1. An adaptive proximity indicating system, utilizing interrogations transmitted by standard azimuthally scanning secondary surveillance radar (SSR) stations and received by a first receiver means, and utilizing reply messages transmitted by transponders replying to such interrogations and received by a second receiver means, for monitoring the proximity of transponders in a particular region of space, said indicating system having a plurality of operating modes for adapting to the signal environment and comprising, in combination:

a. interrogation rate measuring means responsive to said first receiver means for measuring the number of interrogations received per unit of time; and

b. means, responsive to said rate measuring means, for modifying the mode of operation of said indicating system in accordance with the interrogation rate.

2. counter means, responsive to said generator, for accumulating the clock pulses produced by said generator;

and

3. The invention defined in claim 1 wherein said rate measuring means includes means for counting said interrogations for a time substantially equal to the period of rotation of an SSR main beam.

4. The invention defined in claim 1, wherein said indicating system further comprises:

c. indicator means adapted to be actuated in response to the output of said second receiver means;

d. means, responsive to the output of said first receiver means, for preventing actuation of said indicator means during a predetermined first interval, said predetermined first interval being initiated at an instant determined by the time that the wavefront of an interrogation moving at radio velocity passes through an arc having a radius extending from the SSR station transmitting that interrogation to the position of said first receiver means; and

e. means, responsive to said mode modifying means, for changing the length of said predetermined first interval in accordance with the mode of operation.

5. The invention defined in claim 4, wherein said interval length changing means includes means for increasing said length of said first interval in response to an increase in said interrogation rate and decreasing said length of said first interval in response to a decrease in said interrogation rate.

6. The invention defined in claim 1, wherein said indicating system further comprises:

c. indicator means adapted to be actuated in response to the output of said second receiver means;

d. means, responsive to the output of said first receiver means, for preventing actuation of said indicator means after a predetermined second interval, said predetermined second interval being initiated at an instant determined by the time that the wavefront of an interrogation moving at radio velocity passes through an arc having a radius extending from the SSR station transmitting that interrogation to the position of said first receiver means; and

e. means, responsive to said mode modifying means, for changing the length of said predetermined second interval in accordance with the mode of operation.

7. The invention defined in claim 6, wherein said interval length changing means includes means for decreasing said length of said second interval in response to an increase in said interrogation rate and increasing said length of said second interval in response to a decrease in said interrogation rate.

8. The invention defined in claim 1, wherein said indicating system further comprises:

c. indicator means adapted to be actuated in response to the output of said second receiver means;

d. means, responsive to the output of said first receiver means, for preventing actuation of said indicator means during a predetermined first interval and after a predetermined second interval, said predetermined first interval and said predetermined second interval being initiated at an instant determined by the time that the wavefront of an interrogation moving at radio velocity passes through an arc having a radius extending from the SSR station transmitting that interrogation to the position of said first receiver means; and

e. means, responsive to said mode modifying means, for changing the length of one of said predetermined first and second intervals in accordance with the mode of operation.

9. The invention defined in claim 8, wherein said interval length changing means includes means for decreasing length of said second interval in response to an increase in said interrogation rate and increaSing the length of said second interval in response to a decrease in said interrogation rate.

10. The invention defined in claim 1, wherein said indicating system further comprises:

c. indicator means adapted to be actuated in response to the output of said second receiver means;

d. means responsive to the output of said second receiver means for decoding altitude from said reply messages;

e. means responsive to said altitude decoding means for preventing actuation of said indicator means if the decoded altitude does not fall within a prescribed altitude range; and

f. means responsive to said mode modifying means for changing said prescribed altitude range in accordance with the mode of operation.

11. The invention defined in claim 10, wherein said altitude range changing means includes means for decreasing the size of said altitude range in response to an increase in the said interrogation rate and increasing the size of said altitude range in response to a decrease in the said interrogation rate.

12. The invention defined in claim 1, wherein said indicating system further comprises:

c. transmitter means, responsive to the output of said first receiver means, for transmitting a reply message to a received interrogation;

d. means, responsive to the output of said first receiver means, for preventing the reception of reply messages by said second receiver means during the period that a reply message is transmitted; and

e. means, responsive to said mode modifying means and connected to means (c) and means (d), for suppressing the transmission of a reply message and permitting the reception of reply messages during a prescribed period in accordance with the mode of operation.

13. The invention defined in claim 12, wherein said suppression means includes means for suppressing the transmission of a reply message for a non-synchronous period of approximately 2,500 microseconds, approximately 18 times per second.

14. The invention defined in claim 12, wherein said suppression means includes means for suppressing the transmission of a reply message for a period of approximately 100 microseconds after receipt of an interrogation, approximately 18 times per second.

15. The invention defined in claim 1, wherein said indicating system further comprises:

c. indicator means adapted to be actuated in response to the output of said second receiver means;

d. timing means, responsive to the output of said first receiver means, for producing a signal when the main beam of the SSR is directed within a selected azimuth sector of its full rotation; and

e. means responsive to said mode modifying means for changing said selected azimuth sector in accordance with the mode of operation.

16. The invention defined in claim 1, wherein said indicating system further comprises:

c. indicator means adapted to be actuated in response to the output of said second receiver means;

d. timing means, responsive to the output of said first receiver means, for producing a signal when the main beam of the SSR is directed within a selected azimuth sector of its full rotation; and

e. means responsive to said mode modifying means for increasing said selected azimuth sector when said interrogation rate is decreased and decreasing said selected azimuth sector when said interrogation rate is increased.

17. The invention defined in claim 1, wherein said indicating system further comprises:

c. transmitter means for transmitting a signal for causing nearby transponders to transmit a reply message, said transmitter means being responsive to said mode modifying means to enable the transmission in accordance with the mode of operation; and

d. timer means, responsive to said transmitter means and to said second receiver means, for determining the round trip transmission time to said nearby transponders.

18. The invention defined in claim 1, wherein said indicating system further comprises:

c. tranSmitter means for transmitting a signal for causing nearby transponders to transmit a reply message, said transmitter means being responsive to said mode modifying means to enable repetitive transmissions when said interrogation rate falls below a prescribed value; and

d. timer means, responsive to said transmitter means and to said second receiver means, for determining the round trip transmission time to said nearby transponders.

19. The invention defined in claim 1, wherein said indicating system further comprises:

c. filter means, responsive to said first receiver means, for selecting interrogations having a prescribed pulse repetition frequency range; and

d. means, responsive to said mode modifying means, for changing said prescribed frequency range thereby to increase or decrease the number of selected interrogations in accordance with the mode of operation.

20. The invention defined in claim 1, wherein said indicating system further comprises:

c. filter means, responsive to said first receiver means, for selecting interrogations having a prescribed pulse repetition frequency range; and

d. means, responsive to said mode modifying means, for increasing said frequency range when said interrogation rate is decreased and decreasing said frequency range when said interrogation rate is increased.

21. The invention defined in claim 1, wherein said first receiver means includes means for receiving said lobe suppression (SLS) signals with two values of gain and provides said SLS signals at a normal gain output and a high gain output;

c. and wherein said indicating system further comprises;

means coupled to said normal and high gain outputs for providing a continuous pulse train which is synchronized with said SLS signals; and

d. means responsive to said mode modifying means for decoupling means (c) from at least one of said normal and high gain outputs;

whereby said continuous pulse train may be utilized by said indicating system to synchronize said system with the SSR ground station transmitting said SLS signals.

22. The invention defined in claim 21, wherein said two values of gain of said first receiver means are approximately 72-dbm and 85-dbm.

23. An adaptive proximity indicating system utilizing interrogations transmitted by standard azimuthally scanning secondary surveillance radar (SSR) stations and received by a first receiver means, and utilizing reply messages transmitted by transponders replying to such interrogations and received by a second receiver means, for monitoring the proximity of transponders in a particular region of space, said indicating system having a plurality of operating modes for adapting to the signal environment and comprising, in combination:

a. reply rate measuring means responsive to said second receiver means for measuring the number of reply messages received per unit of time; and

b. means, responsive to said rate measuring means, for modifying the mode of operation of said indicating system in accordance with the reply rate.

24. An adaptive proximity indicating system, utilizing interrogations transmitted by standard secondary surveillance radar (SSR) stations and reply messages transmitted by transponders replying to such interrogations, for monitoring the proximity of transponders in a particular region of space, said indicating system having a plurality of operating modes for adapting to the signal environmennt and comprising, in combination:

a. first receiver means for receiving said interrogations;

b. second receiver means for receiving said reply messages;

c. first rate measuring means responsive to said first receiver means for measuring the number of interrogations received per unit of time;

d. second rate measuring means responsive to said second receiver means for measuring the number of reply messages received per unit of time;

e. means responsive to said first rate measuring means for modifying the mode Of operation of said indicating system in accordance with the interrogation rate; and

f. means responsive to said second rate measuring means for modifying the mode of operation of said indicating system in accordance with the reply rate.

25. An adaptive proximity indicating system for use in an aircraft, utilizing interrogations transmitted by standard azimuthally scanning secondary surveillance radar (SSR) stations and received by a first receiver means, and utilizing reply messages transmitted by transponders replying to such interrogations and received by a second receiver means, for monitoring the proximity of transponders in a particular region of space, said indicating system having a plurality of operating modes for adapting to the signal environment and comprising, in combination:

a. means for measuring the altitude of the aircraft; and

b. means, responsive to said altitude measuring means, for modifying the mode of operation of said indicating system in accordance with the altitude.

26. An adaptive proximity indicating system, utilizing interrogations and side lobe suppression (SLS) signals transmitted by standard azimuthally scanning secondary surveillance radar (SSR) stations and received by a first receiver means, and utilizing reply messages transmitted by transponders replying to such interrogations and received by a second receiver means, for monitoring the proximity of transponders in a particular region of space, said indicating system having a plurality of operating modes for adapting to the signal environment and comprising, in combination:

a. means responsive to said first receiver means for decoding said SLS signals; and

b. means, responsive to said decoding means, for modifying the mode of operation of said indicating system in accordance with the strength of said SLS signals.

27. An adaptive proximity indicating system, utilizing interrogations transmitted by standard azimuthally scanning secondary surveillance radar (SSR) stations and reply messages transmitted by transponders replying to such interrogations, for monitoring the proximity of transponders in a particular region of space, said indicating system having a plurality of operating modes for adapting to the signal environment and comprising, in combination:

a. first receiver means for receiving said interrogations;

b. second receiver means for receiving said reply messages;

c. means, responsive to said first and second receiver means, for determining the time of arrival (TOA) of each reply message of a given transponder initiated by an interrogation from each SSR station received, said TOA'"'"''"'"'s being measured relative to an instant determined by the time that the wavefront of an interrogation moving at radio velocity passes through an arc having a radius extending from the SSR station transmitting that interrogation to the position of said first receiver means;

d. means for measuring the rate of determination of the TOA'"'"''"'"'s for said given transponder; and

e. means, responsive to said rate measuring means, for modifying the mode of operation of said indicating system in accordance with said rate.

28. The invention defined in claim 27, wherein said rate measuring means includes means for counting the number of times a rotating main beam of an SSR station is received during a prescribed period of time.

29. The invention defined in claim 27, wherein said rate measuring means includes means for counting said TOA'"'"''"'"'s determined for a time substantially equal to the period of rotation of an SSR main beam.

30. The invention defined in claim 27, wherein said indicating system further comprises:

f. means for transmitting a signal for causing nearby transponders to transmit a reply message, said transmitter means being responsive to said mode modifying means to enable the transmission in accordance with the mode of operation; and

g. timer means, responsive to said transmitter means and to said second receiver means, for determining the round trip transmission time to nearby transponders.

31. The invention defined in claim 27, wherein said indicating system further comprises:

f. means for transmitting a signal for causing nearby transponders to transmit a reply message, said transmitter means being responsive to said mode modifying means to enable repetitive transmissions when said rate falls below a prescribed value; and

g. timer means, responsive to said transmitter means and to said second receiver means, for determining the round trip transmission time to nearby transponders.

32. The invention defined in claim 27, wherein said indicating system further comprises:

f. means, responsive to said TOA-determining means, for storing a plurality of TOA'"'"''"'"'s;

g. means, responsiive to said storage means, for selecting the largest TOA that is stored; and

h. means, responsive to said mode modifying means and to said selecting means, for producing a signal representing the largest TOA in accordance with the mode of operation.

33. The invention defined in claim 27, wherein said indicating system further comprises:

f. means, responsive to said TOA-determining means, for storing a plurality of successive TOA'"'"''"'"'s determined for a given transponder in a prescribed period of time;

g. means, responsive to said storage means, for selecting the largest TOA that is stored; and

h. means, responsive to said mode modifying means and to said selecting means, for producing a signal representing the largest TOA in accordance with the mode of operation.

34. The invention defined in claim 27, wherein said indicating system further comprises:

f. means, responsive to said TOA-determining means, for storing a plurality of successive TOA'"'"''"'"'s determined for a given transponder during a period time substantially equal to the period of rotation of an SSR main beam;

g. means, responsive to said storage means, for selecting the largest TOA that is stored; and

h. means, responsive to said mode modifying means and to said selecting means, for producing a signal representing the largest TOA in accordance with the mode of operation.

35. The invention defined in claim 27, wherein said indicating system further comprises:

f. means, responsive to said TOA-determining means, for storing a plurality of successive TOA'"'"''"'"'s determined for a given transponder in a prescribed period of time;

g. means, responsive to said storage means, for selecting the largest TOA that is stored; and

h. means, responsive to said mode modifying means and to said selecting means, for producing a signal representing the largest TOA in accordance with the mode of operation, if the number of TOA'"'"''"'"'s stored in said storage means for said prescribed period of time exceeds a given value.

36. A common azimuthal sector proximity indicating system, utilizing interrogationsn transmitted by a standard azimuthally scanning secondary surveillance radar (SSR) station and reply messages transmitted by a transponder replying to such interrogations, for monitoring the proximity of transponders in an azimuth sector wider than the rotating main beam of the radar, comprising:

a. first receiver means for receiving said interrogations during the passage of the rotating main beam, b. second receiver means for receiving said reply messages transmitted by said transponder as it is interrogated by the rotating main beam, c. timing means, responsive to said first receiver means, for producing a control signal when the rotating main beam is directed within a selected azimuth sector of its full rotation, said timing means including;

37. The invention set forth in claim 36, wherein said generator includes a phase locked oscillator which operates synchronously with the pulse repetition frequency of said interrogations.

38. The invention set forth in claim 37, further comprising timer means, responsive to said generator, to said second receiver means and to said comparator means, for determining the time of arrival (TOA) of reply messages transmitted by said transponder when said control signal is present, said TOA'"'"''"'"'s being measured relative to the clock pulses produced by said generator.

39. The invention defined in claim 37, further comprising e. decoder means, responsive to said generator, to said second receiver means and to said comparator means, for decoding a reply solicitation encoded in reply messages transmitted by said transponder when said control signal is present;

and f. transmitter means responsive to said decoder means for transmitting a range reply signal when a reply solicitation has been decoded.

40. The invention defined in claim 39, wherein said timing means further includes means for selecting said reference count range such that said control signal is produced by said comparator means for a period immediately prior to the arrival of the leading edge of the rotating main beam.

41. The invention defined in claim 39, wherein said timing means further includes means for selecting said reference count range such that said control signal is produced by said comparator means for a period immediately after the passage of the trailing edge of the rotating main beam.

42. The invention set forth in claim 36, wherein said timing means further includes means for resetting said counter means once during each revolution of said main beam.

43. A proximity indicating system utilizing interrogations transmitted by standard azimuthally scanning secondary surveillance radar (SSR) stations and reply messages transmitted by transponders replying to such interrogations, for monitoring the proximity of transponders in a particular region of space, said indicating system comprising in combination:

a. first receiver means for receiving said interrogations;

b. second receiver means for receiving said reply messages;

c. a plurality of storage means;

d. gating means, responsive to the output of said second receiver means, for selectively coupling the output of said second receiver means to one of said storage means;

e. gate actuating means, responsive to the output of said first receiver means, for causing said gating means to couple the output of said second receiver means to successive ones of said storage means at successive predetermined intervals, said predetermined intervals being initiated at an instant determined by the time that the wavefront of an interrogation moving at radio velocity passes through an arc having a radius extending from the SSR station transmitting that interrogation to the position of said first receiver means;

f. indicator means; and

g. means for coupling the output of at least one of said storage means to said indicator means.

44. The proximity indicating system defined in claim 43, further comprising:

h. interrogation rate measuring means responsive to said first receiver means for measuring the number of interrogations received per unit of time;

wherein means (g) includes means, responsive to said interrogation rate measuring means, for changing the outputs of said storage means which are coupled to said indicator means in accordance with the interrogation rate.

45. The proximity indicating system defined in claim 43, further comprising:

h. reply rate measuring means responsive to said second receiver means for measuring the number of reply messages received per unit of time;

wherein means (g) includes means, responsive to said reply rate measuring means, for changing the outputs of said storage means which are coupled to said indicator means in accordance with the reply rate.

46. The proximity indicating system defined in claim 43, wherein means (g) includes manually operable gating means for changing the outputs of said storage means which are coupled to said indicator means.