Radio navigational aid with separate standard frequency signal

Abstract

Radio guidance signals comprising a carrier having modulation patterns defining a predetermined guidance path plane for a craft to be guided are transmitted, preferably in a scanning beam, from a ground station. A separate standard frequency signal is also transmitted from the ground station which has a predetermined difference in frequency from the guidance signal carrier frequency, the standard frequency being employed to control a local oscillator at the receiver.

I claim: 
     
       1. An improved guidance method for a craft to be guided including transmitting radio guidance signals from a ground station comprising a carrier having modulation .[.patters.]. .Iadd.patterns .Iaddend.defining a predetermined guidance path plane for a craft to be guided,   transmitting a separate standard frequency signal from the ground station having a predetermined difference in frequency from the guidance signal carrier frequency,   and employing the standard frequency to control a local oscillator within a receiver in the craft to be guided to improve the discrimination function of the receiver is discriminating the desired guidance signals from other signals.   
     
     
       2. A method as claimed in claim 1 wherein the standard frequency is employed in the receiver to generate control signals to control the local receiver oscillator to thereby lock the frequency of the oscillator in a fixed frequency relationship to the standard frequency. 
     
     
       3. A method as claimed in claim 2 wherein the frequency lock condition is detected and used to gate guidance signals through the receiver to provide guidance information to the operator of the craft to be guided. 
     
     
       4. A radio guidance method comprising transmitting a pattern of radio carrier signals in a scanning beam with different portions of the scanning beam being positioned on opposite sides of a guidance path plane and carrying modulation to define the guidance path plane for a craft to be guided,   transmitting a standard radio frequency signal providing substantially uniform radiation over the entire sector covered by the scanning beam while the scanning beam is being transmitted,   the standard frequency signal having a predetermined difference in frequency from the radio carrier frequency of the scanning beam for controlling a receiver local oscillator in the craft to be guided for .[.enhacing.]. .Iadd.enhancing .Iaddend.the signal discrimination function.   
     
     
       5. A method as claimed in claim 4 wherein the radio carrier signals are transmitted in a switched scanning beam with different individual and distinct switched portions of the scanning beam carrying unique modulation to define the guidance path plane.   
     
     
       6. A method as claimed in claim 5 wherein the individual switched portions of the scanning beam are modulated by controlling the duration of the pulse of carrier frequency energy radiated for each portion of the scanning beam.   
     
     
       7. A method as claimed in claim 4 wherein the standard frequency signal is transmitted on a higher duty cycle than any one of the different portions of the scanning beam.   
     
     
       8. A method as claimed in claim 7 wherein the standard radio frequency signal is transmitted as a continuous wave.   
     
     
       9. A method for transmitting radio guidance signals comprising transmitting a pattern of signals in a switched scanning beam with individual and distinct switched portions of the scanning beam being positioned on opposite sides of a guidance path plane by switching the radio frequency energy in a dispersed position sequence from one switched portion to another so that the signal from each individual switched portion is intermittent in nature,   and modulating the scanning beam with two different modulation signals by providing different ratios of the respective amounts of modulation by said two different modulation signals for said distinct switched portions of the scanning beam with the variation of the modulation ratio being substantially symmetrical about the guidance path plane so that said modulation signals are respectively dominant on opposite sides of the plane and the value of the ratio is one at the plane to thereby define the guidance path plane.   
     
     
       10. A method as claimed in claim 9 wherein the dispersed position sequence is one in which successive switched portions of the scanning beam are always radiated from positions mutually displaced by at least two scanning beam switched portion positions.   
     
     
       11. A method as claimed in claim 9 wherein the dispersed position sequence is one in which successive switched portions of the scanning beam are always radiated from positions mutually displaced by at least three scanning beam switched portion positions.   
     
     
       12. A radio guidance signal transmitter comprising means for transmitting a pattern of radio carrier signals in a scanning beam with different portions of the scanning beam being positioned on opposite sides of a guidance path plane, means for modulating the portions of the scanning beam positioned on opposite sides of the guidance path plane to thereby define the guidance path plane in terms of guidance signals for a craft to be guided,   and means for transmitting a standard radio frequency .[.10.]. signal in a substantially uniform pattern of radiation over the entire sector of space covered by the scanning beam,   the standard frequency signal having a predetermined difference in frequency from the radio carrier frequency of the scanning beam for controlling the local oscillator of a receiver.   
     
     
       13. A transmitter as claimed in claim 12 wherein said means for transmitting a pattern of radio carrier signals comprises a plurality of antenna elements and switching means for switching radio carrier signals from one antenna element to another to thereby provide individual and distinct switched portions of the scanning beam to form a switched scanning beam,   and means for individually modulating the different switched portions of the scanning beam to define the guidance path plane.   
     
     
       14. A transmitter as claimed in claim 13 wherein said modulating means is a pulse modulation means operable in synchronism with the switching of the different portions of the scanning beam to said different antenna elements and operable to control the duration of each period of transmission of energy from each of said antenna elements to thereby provide modulation information in each pulse of carrier energy transmitted from each antenna element. 
     
     
       15. A transmitter as claimed in claim 13 wherein said means for transmitting said standard frequency signal is operable upon a higher duty cycle than any one of the different switched portions of the scanning beam.   
     
     
       16. A transmitter as claimed in claim 15 wherein said means for transmitting said standard frequency signal comprises an antenna element separate from said different antenna elements comprising said means for transmitting said switched portions of said scanning beam,   said means for transmitting said standard frequency signal being operable on a continuous basis to transmit a continuous wave signal. .Iadd. 17. A method for transmitting radio guidance signals comprising   transmitting a pattern of signals in a switched scanning beam with individual and distinct switched portions of the scanning beam being arranged in different positions on opposite sides of a guidance path plane by switching the radio frequency energy in a dispersed position sequence from one switched portion to another so that the signal from each individual switched portion comprises intermittent pulses of carrier frequency energy,   and modulating the individual switched portions of the scanning beam to define the guidance path plane by controlling the duration of each pulse of carrier frequency energy radiated for each portion of the scanning beam. .Iaddend..Iadd. 18. A method as claimed in claim 17 wherein   the scanning beam is modulated with two different modulation signals by providing different ratios of the respective amounts of modulation by said two different modulation signals for said distinct switched portions of the scanning beam with the variation of the modulation ratio being such that said modulation signals are respectively dominant on opposite sides of the guidance path plane and the value of the ratio is one at the plane to thereby define the guidance path plane. .Iaddend..Iadd. 19. A method as claimed in claim 17 including   transmitting a standard radio frequency signal providing substantially uniform radiation over the entire sector covered by the scanning beam while the scanning beam is being transmitted,   the standard frequency signal having a predetermined difference in frequency from the radio carrier frequency of the scanning beam for controlling a receiver oscillator in the craft to be guided for enhancing the signal discrimination function. .Iaddend.