Proximity indication with range and bearing measurements

Abstract

Proximity indication and evaluation for aircraft, using only the signals emitted by secondary surveillance radar and cooperating transponders, to detect intrusion in a monitored proximity volume and determine slant range and relative bearing to the intruder.

I claim: 
     
       1. A method of determining at an own transponder station the bearing angle φ of said own station from a selected .Iadd.one of a plurality of .Iaddend.secondary surveillance .[.radar.]. .Iadd.radars .Iaddend.(SSR) that .Iadd.transmit directional interrogation signals of the same frequency and that .Iaddend.omniazimuthally .[.transmits a.]. .Iadd.transmit .Iaddend.reference .[.signal.]..Iadd.signals .Iaddend.as the main radar .[.beam sweeps.]. .Iadd.beams thereof sweep .Iaddend.through a standardized reference direction, such as magnetic North, said method comprising the steps of: (a) receiving said reference signals .[.,.]. .Iadd.from said radars, .Iaddend.   (b) receiving interrogation signals from said .[.radar.]. .Iadd.radars .Iaddend.as the main .[.beam sweeps.]. .Iadd.beams thereof sweep .Iaddend.by the own location,   (c) .[.measuring the time interval between successive reception of one of said reference and said interrogation signals and producing a quantitative first representation of the main beam rotation interval,.]. .Iadd.selecting the reference and interrogation signals received from one of said secondary surveillance radars, .Iaddend.   (d) .[.measuring and producing a quantitative second representation of the time interval between reception of a reference signal and reception of the next subsequently received interrogation signal,.]. .Iadd.measuring the time interval between successive reception of one of said selected reference and said selected interrogation signals and producing a quantitative first representation of the main beam rotation interval, .Iaddend.   (e) .[.dividing the value of said second representation by that of said first representation to produce the quotient of said values, and.]. .Iadd.measuring and producing a quantitative second representation of the time interval between reception of one of said selected reference and said selected interrogation signals and the next subsequently received other one of said signals, .Iaddend.   (f) .[.producing a quantitative representation φ of said quotient..]. .Iadd.dividing the value of said second representation by that of said first representation to produce the quotient of said values, and   (g) producing a quantitative representation φ of said quotient. .Iaddend.   
     
     
       2. Apparatus for determining at an own transponder station the bearing angle φ of said own station from a selected .[.azimuthally scanning radar that omnidirectionally transmits a.].  .Iadd.one of a plurality of secondary surveillance radars (SSR) that transmit directional interrogation signals of the same frequency and that omniazimuthally transmit .Iaddend.reference .[.signal when its directional beam points in a standard.]. .Iadd.signals as the main radar beams thereof sweep through a standardized .Iaddend.reference direction, such as .Iadd.magnetic .Iaddend.North, said apparatus comprising: (a) means for receiving said reference .[.signal.]. .Iadd.signals .Iaddend.and for receiving the .[.normal.]. interrogation transmission signals of said .Iadd.radars .Iaddend.as the radar .[.beam sweeps.]. .Iadd.beams sweep .Iaddend.by the own location,   (b) .[.a first interval timer for measuring the interval between successive reception of one of said reference and said normal transmission signals and producing a quantitative representation N of said interval,.]. .Iadd.means for selecting the reference and interrogation signals received from one of said secondary surveillance radars, .Iaddend.   (c) .[.a second interval timer for measuring and producing quantitative representation M of the interval between reception of a reference signal and a normal transmission signal,.]. .Iadd.a first interval timer for measuring the interval between successive reception of one of said selected reference and said selected interrogation signals and producing a quantitative representation N of said interval, .Iaddend.   (d) .[.divider means for computing the quotient M/N, and.]. .Iadd.a second interval timer for measuring and producing a quantitative second representation M of the time interval between reception of one of said selected reference and said selected interrogation signals and the next subsequently received other one of said signals, .Iaddend.   (e) .[.means for producing a quantitative representation φ of said quotient..]. .Iadd.divider means for computing the quotient M/N, and   (f) means for producing a quantitative representation φ of said quotient. .Iaddend.   
     
     
       3. A method as in claim 1 for additionally producing at said own transponder station a representation of the angular relationship between the bearing of said own transponder station from said selected SSR and the bearing from said selected SSR of another transponder station within a common azimuthal sector with said own transponder station, including the further steps of: .[.(g).]. .Iadd.(h) .Iaddend.receiving at said own transponder station reply signals transmitted by said other transponder station in response to said interrogation signals as said main beam sweeps by said other transponder station,   .[.(h).]. .Iadd.(i) .Iaddend.determining the time relationship between said interrogation signals and said reply signals, and   .[.(i).]. .Iadd.(j) .Iaddend.producing, in accordance with said time relationship, a representation of said angular relationship between said bearing angles from said selected SSR.   
     
     
       4. The method according to claim 3 wherein step .[.(i).]. .Iadd.(j) .Iaddend.comprises the steps of: .[.(j).]. .Iadd.(k) .Iaddend.producing a lead signal in response to the prior occurrence of said interrogation signals immediately subsequent ot said reference signals, and   .[.(k).]. .Iadd.(1) .Iaddend.producing a lag signal in response to the prior occurrence of said reply signals immediately subsequent to said reference signals.   
     
     
       5. Apparatus according to claim 2 for additionally producing at said own transponder station a representation of the angular relationship between the bearing of said own transponder station from said selected SSR and the bearing from said selected SSR of another transponder station within a common azimuthal sector with said own transponder station, further comprising: .[.(f).]. .Iadd.(g) .Iaddend.means for receiving at said own transponder station reply signals transmitted by said other transponder station in response to said interrogation signals as said main beam sweeps by said other transponder station,   .[.(g).]. .Iadd.(h) .Iaddend.means for determining the time relationship between said interrogation signals and said reply signals, and   .[.(h).]. .Iadd.(i) .Iaddend.means for producing, in accordance with said time relationship, a representation of said angular relationship between said bearing angles from said selected SSR.   
     
     
       6. Apparatus according to claim 5 wherein the means .[.(h).]. .Iadd.(i) .Iaddend.comprises: .[.(i).]. .Iadd.(j) .Iaddend.means for producing a lead signal in response to the prior occurrence of said interrogation signals immediately subsequent to said reference signals, and   .[.(j).]. .Iadd.(k) .Iaddend.means for producing a lag signal in response to the prior occurrence of said reply signals immediately subsequent to said reference signals. .Iadd. 7. The method according the claim 1 wherein the reference and interrogation signals are selected in accordance with the pulse repetition characteristic associated with said one of said secondary surveillance radars. .Iaddend. .Iadd. 8. The apparatus according to claim 2, wherein means (b) selects the reference and interrogation signals in accordance with the pulse repetition characteristic associated with said one of said secondary surveillance radars. .Iaddend.