Scanning beam radio navigation method and apparatus

• US 4,080,600 A
• Filed: 12/03/1976
• Issued: 03/21/1978
• Est. Priority Date: 05/20/1976
• Status: Expired due to Term

• Current Assignee: Wilcox Electric Incorporated
• Original Assignee: TULL Aviation Corporation
• Inventors: Toman, Donald J.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US05/747,244
• Time in Patent Office: 473 Days
• Field of Search: 343/106 R, 343/106 D, 343/108 M
• US Class Current: 342/398
• CPC Class Codes: G01S 1/022 Means for monitoring or calibrating
• CPC Class Codes: G01S 1/024 of beacon transmitters
• CPC Class Codes: G01S 1/38 using comparison of [1] the phase of the envelope of the change of frequency, due to Doppler effect, of the signal transmitted by an antenna moving, or appearing to move, in a cyclic path with [2] the phase of a reference signal, the frequency of this reference signal being synchronised with that of the cyclic movement, or apparent cyclic movement, of the antenna
• CPC Class Codes: G01S 1/44 Rotating or oscillating beam beacons defining directions in the plane of rotation or oscillation

Abstract

High accuracy guidance signals are produced over a wide angle by sequencing in a predetermined sequence through a series of narrow angular sectors while electrically scanning the transmitted signals within each sector.

Claims

1. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

said radio signals transmitted in conjunction with each of said electrically scanned sector signals to uniquely identify the rotational position of said antenna array being transmitted prior to the transmission of the associated electrically scanned sector signals as a part of an information preamble to the sector signals,

the information preamble also including other identifying data distinguishing the wide angle sector angular position function from other functions for which similar signals are transmitted.

2. A method as claimed in claim 1 wherein

said predetermined axis is a horizontal axis and said angular positions are elevation angles.

3. A method as claimed in claim 1 wherein

said predetermined axis is a vertical axis and said angular positions are azimuth angles.

4. A method as claimed in claim 3 wherein

said wide angle sector encompasses the entire 360°

azimuth.

5. A method as claimed in claim 1 wherein

said separate electrically scanned sector signals are produced by separate fixed antenna arrays for each sector.

6. A method as claimed in claim 1 wherein

the information preamble is transmitted by binary digital coding of the carrier signal.

8. A method as claimed in claim 1 wherein

the scanned sector signals are each emitted as a time reference scan group including a "to" scan and a "fro" scan

with the angular position of the receiver being determined on the basis of the time interval between reception of the "to" scan and "fro" scan signals.

10. A method as claimed in claim 1 wherein

the electrically scanned sector signals are blanked out in at least one of the rotational position sectors in order to avoid multipath signal problems arising in that particular sector.

31. A method as claimed in claim 1 wherein

said rotational position identification signals are transmitted over a limited sector generally corresponding to the sector covered by the sector signals.

7. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

and transmitting additional radio signal energy in clearance beams and in side lobe suppression signals in order to enable the receiver to discriminate between valid sector signals for the sector in which the receiver is positioned and sector signals radiated for other sectors.

9. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

the electrically scanned sector signals being scanned by the Doppler method wherein the radiated signal is switched in sequence from one end to the other of an array of radiating elements to convey the impression of radiation from a moving source which moves from one end to the other of the array,

and which creates a frequency shift in a receiver dependent upon the orientation of the receiver with respect to the array.

11. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

receiving said directional radio guidance signals with a receiver in an aircraft to be guided,

storing the true angular position of the receiver relative to the ground station as indicated by at least the last previous radio guidance signal,

and processing the next subsequent guidance signal by decoding the sector identification information associated with that guidance signal,

subtracting the characteristic sector angle associated with the identified sector from said stored true relative angular position and using the difference to set angle limit track gates indicating the angle limits within which a valid sector scan signal should appear within the identified sector,

then using said track gate limits to confirm the validity of the subsequent sector scan signal indicating the angle within the identified sector,

and then adding to the confirmed sector scan signal the characteristic sector angle of the identified sector to provide the true relative angular position as an output to the operator.

12. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

receiving said directional radio guidance signals with a receiver in an aircraft to be guided,

storing the true angular position of the receiver relative to the ground station as indicated by each of a representative plurality of said signals received in sequence,

computing an average value of said true relative angular positions,

setting said receiver into a track mode,

then processing the first subsequent guidance signal by decoding the sector identification information,

subtracting the characteristic sector angle associated with the identified sector from said average value and using the difference to set angle limit track gates indicating the angle limits within which a valid sector scan signal should appear within the identified sector,

then using said track gate limits to confirm the validity of the subsequent sector scan signal indicating the angular position within the identified sector,

and then adding to the confirmed sector scan signal and characteristic sector angle of the identified sector to provide the true relative angular position as an output to the operator.

13. A method as claimed in claim 12 wherein

second and later subsequent guidance signals are processed by storing the last previous true relative angular position output and using that stored output in substitution for said average value in setting the angle limit track gate after subtracting the characteristic sector angle of the identified sector.

14. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

and providing directional information in at least one selected sector in addition to said wide angle sector by means of at least one additional separate electrically scanned sector signal.

15. A method as claimed in claim 14 wherein

said predetermined axis is vertical and said wide angle sector provides forward azimuth course guidance and said additional selected sector provides back azimuth course guidance.

16. A method of providing accurate directional information to an aircraft in any angular position about a predetermined axis over a wide angle sector with respect to a ground station comprising

transmitting radio guidance signals in a sequence of separate electrically scanned sector signals in limited angle sectors within said wide angle sector,

transmitting radio signals in conjunction with each of said separate electrically scanned sector signals to uniquely identify the particular sector,

the number of said separate sectors at which electrically scanned sector signals are emitted being sufficient to cover all angular positions within said wide angle sector by the combination of all of the separate electrically scanned sector signals,

mechanically rotating about said predetermined axis a ground station transmitter antenna array which is capable of producing directional radio guidance signals by an electrical scan through only one of said limited angle sectors for each rotational position thereof,

and transmitting from the antenna array said sequence of separate electrically scanned sector signals during successive mechanical rotation through a plurality of separate rotational positions,

the identification radio signals transmitted in conjunction with each of said electrically scanned sector signals being operable to uniquely identify the rotational position of said antenna array corresponding to a particular sector.

17. A method as claimed in claim 16 wherein

the scanned sector signals are each emitted as a time reference scan group including a "to" scan and a "fro" scan,

with the angular position of the receiver being determined on the basis of the time interval between reception of the "to" scan and "fro" scan signals.

18. A method as claimed in claim 17 wherein

the electrical scanning of the sector signals is carried out in a substantially circular sector and in which the effective axis of the electrical scan is displaced from the axis of mechanical rotation of the antenna array in order to provide for multipath discimination as the signals are received.

19. A method as claimed in claim 17 wherein the electrical scanning rates of the "to" and "fro" scans are different to provide rotational scan rate compensation for the mechanical rotation of the antenna array so as to provide "to" and "fro" scans having the same absolute rate of rotation in the two different scan directions.

20. A method as claimed in claim 19 wherein the "to" and "fro" scans are position compensated so that the angles at which the electrical scans respectively for "to" and "fro" are commenced at different angles with respect to the rotating antenna array in order to compensate for the mechanical displacement of the mechanically rotating antenna array in the interval between the commencement of the "to" scan and the commencement of the "fro" scan.

21. A method as claimed in claim 16 wherein

the scanned sector signals are monitored by a fixed monitor receiver which is arranged to receive scanned sector signals in only one of the antenna sectors.

22. Radio guidance apparatus for providing accurate orientation information to an aircraft in any angular position over a wide angle sector with respect to a predetermined axis at a ground station comprising

a ground station including a transmitter and an associated antenna array which is capable of producing directional radio guidance signals by an electrical scan through only a limited angle sector,

platform means for supporting and mechanically rotating said antenna array about said predetermined axis to thereby change the orientation of said antenna array,

said ground station being capable of transmitting radio guidance signals from said antenna array in a sequence of separate electrically scanned sector signals during successive mechanical rotation through a plurality of different rotational positions,

the number of said different rotational positions at which electrically scanned sector signals are emitted being sufficient to cover all angles within said wide angle sector by the combination of all of the electrically scanned sector signals,

said apparatus including means for transmitting radio signals in conjunction with each of said electrically scanned sector signals to uniquely identify the rotational position of said antenna array corresponding to a particular sector.

23. Apparatus as claimed in claim 22 wherein

all of the directions about said axis are divided into a predetermined number of fixed sectors having predetermined sector width,

and wherein there is provided a means for detecting the rotation of said antenna array through said different sectors,

said transmitter being connected to said last-named means and being operable in response to detection of the rotation of said antenna array from one sector to another to initiate a sector scan signal for the new sector.

24. Apparatus as claimed in claim 23 wherein

said transmitter is rotatable with said antenna array, and wherein said means for detecting the rotation of said antenna array from one sector to another comprises

a photo responsive pick-up means rotatable with said transmitter and said antenna array and a cooperating fixed optical track having optical characteristics which are different at different sectors.

25. Apparatus as claimed in claim 22 wherein

there is provided a monitor receiver apparatus to receive and monitor the sector scan signals in at least one predetermined sector to thereby monitor the accuracy of the sector scan,

and switching means operable for detection of the rotation of said antenna array into the monitored sector for activating said monitor apparatus.

26. Apparatus as claimed in claim 25 wherein

said monitor apparatus includes a plurality of receiver antennas positioned at different angles within the monitored sector for accurately monitoring the sector scan signals within the entire sector.

27. Apparatus as claimed in claim 22 wherein

said transmitter and said antenna array are operable to produce the electrical scan through the limited angle sector by scanning a beam of energy to and fro so that the receiver can detect position by measuring the interval between the reception of the respective to and fro scan signals.

28. Apparatus as claimed in claim 22 wherein

said antenna array is a straight line Doppler array which is operable to provide the sector scan signal by the Doppler principle.

29. An aircraft receiver apparatus for receiving directional radio guidance signals including a sector scan signal in each of a series of different narrow angular sectors about a predetermined axis at a ground station from which the signals are transmitted and in which the sectors together may cover all possible angular positions of said aircraft about said axis to provide signals giving the true angular position to the aircraft carrying the receiver,

each sector scan signal including sector identification information,

said receiver including means for storing the true angular position of the receiver relative to the ground station as indicated by at least the last previous radio guidance signal,

means for processing the next subsequent guidance signal by decoding the sector identification information associated with that guidance signal,

means for subtracting a characteristic sector angle associated with the identified sector from said stored true angular position,

angle limit track gates and means for employing the difference to set said angle limit track gates to indicate the angle limits within which a valid sector scan signal should appear within the identified sector,

and means for adding the characteristic sector angle of the identified sector to a sector scan signal which is confirmed as valid by said track gates to thereby provide the true angular position as an output,

and indicating means connected to receive said true angular position for display.

30. An aircraft receiver as claimed in claim 29 wherein

said storing means for said true angular position comprises means for storing the true angular position of the receiver relative to the ground station as indicated by each of a representative plurality of sector scan signals received in sequence and means for computing an average value of said true relative angular positions,

said storing means being operable for storing said average value for use as said stored true angular position for setting said angle limit track gates.