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Title: Multiple beam glide slope radio navigation method with two classes of beams
Claims: claim: 1. A method of radiating a pattern of navigation guidance signals to an aircraft to define a glide path with a minimum of distortion from the terrain and structures beneath the guidance signal pattern comprising transmitting the signals in a pattern of beams of radio carrier frequency energy with different beams positioned at different angles above and below the guidance path, switching carrier frequency energy in a sequence from one beam to another to radiate energy in all of the beam positions to establish the pattern of beams, applying a program of modulation to the radio carrier frequency energy for each of said beams to define the glide slope path, said beams comprising a class of upper beams and a class of lower beams positioned beneath said upper beams, said class of upper beams consisting of a plurality of beams of uniform angular width in elevation and having a uniform angular center-to-center beam spacing in elevation, said class of lower beams consisting of at least one beam, each beam of said lower beams having a reduced angular width in elevation which is a single predetermined fraction of the width of each of said upper beams, each of said lower beams having a center line angular spacing in elevation beneath the center line of the next higher beam which is generally reduced from the spacing between said upper beams in proportion to the reduced beam width, the peak energy radiated at the center lines of each of said upper beams being substantially uniform, the peak energy radiated at the center lines of each of said lower beams being proportional to the peak energy radiated in each of said upper beams, the proportion being an inverse function of the respective beam widths. 2. A method as claimed in claim 1 wherein said sequence of switching of carrier frequency energy is carried out by energizing all beams of said class of upper beams the same number of times in each switching sequence and by energizing each beam of said class of lower beams by a number of times less than the number of energizing times for each of said upper beams and having an inverse proportional relationship to the peak energy radiated in each lower beam versus the peak energy radiated in each of said upper beams to thereby provide for substantially uniform signal radiation energy at all elevation radiation angles within the radiation pattern. 3. A method as claimed in claim 2 wherein said class of lower beams consists of at least two beams. 4. A method as claimed in claim 3 wherein the lowermost beam of said lower beams is reduced in peak energy level to reduce reflections from obstructions and to thereby reduce distortion of the signal pattern while maintaining fly up clearance signals in the near range. 5. A method as claimed in claim 3 wherein each beam of said class of lower beams has an angular width in elevation substantially equal to one-half the angular width in elevation of each beam of said class of upper beams. 6. A method as claimed in claim 5 wherein each beam of said class of upper beams has an angular beam width in elevation of less than two degrees and each beam of said class of lower beams has an angular beam width in elevation of less than one degree when the margins of each beam for determining beam width are defined as the positions on the beam contours which are down three decibels in signal strength from the peak signal strength at the beam center line. 7. A method as claimed in claim 5 wherein said class of upper beams consists of three beams and said class of lower beams consists of two beams. 8. A method as claimed in claim 2 wherein said carrier frequency energy is radiated at microwave frequencies. 9. A method as claimed in claim 2 wherein the carrier frequency energy is modulated by controlling the duration of the burst of carrier frequency energy radiated at each beam position during each switching sequence to thereby provide pulse duration modulation of the carrier frequency in each beam position. 10. A method as claimed in claim 1 wherein the modulation applied to the radio carrier energy signifies two different fixed tone modulation frequencies respectively signifying fly up and fly down information, said modulation for fly up and fly down information being applied to the different beams in different relative proportions to provide a predominance of fly up signal below the glide path and a predominance of fly down signal above the glide path. 11. A method as claimed in claim 1 wherein all of the separate beams are radiated directionally with a fan shape which is wide in the horizontal and narrow in the vertical direction. 12. A method as claimed in claim 1 including aligning a multiple element antenna array to provide a separate beam of carrier signal radiation from each element to thereby form the pattern of beams, mechanically adjusting the angular position of the entire multiple element antenna array so that the element producing the lowermost beam is aimed high enough to avoid any substantial line-of-sight obstruction to the lowermost beam to minimize reflections from the obstruction while substantially filling the air space above the obstruction with a guidance signal, and modifying the program of modulation for each of said beams to re-establish the glide slope path having the desired glide slope angle while compensating for the mechanical adjustment of the antenna array. 13. A method as claimed in claim 12 wherein the separate beams are radiated from separate slotted wave guide radiation elements. 14. A method as claimed in claim 13 wherein the wave guide radiation elements are physically arranged at different relative angles to provide the radiation of the pattern of beams spaced at different angles above the horizon. 15. Apparatus for radiating a pattern of navigation guidance signals to an aircraft to define a glide path with a minimum of distortion from the terrain and structures beneath the guidance signal pattern comprising a plurality of antenna elements, each element being operable to transmit a separate beam of radio carrier frequency radiation to thereby form a pattern of beams of carrier energy with different beams spaced at different angles above and below the guidance path, means for switching carrier frequency energy in a sequence from one element to another to radiate energy in all of the beam positions to establish the pattern of beams, means for applying a program of modulation to the carrier energy switched to each of said elements to define the glide slope path, said antenna elements comprising at least two different classes including a class for producing upper beams and a class for producing lower beams positioned beneath the upper beams, said class of upper beam elements consisting of a plurality of elements operable to produce beams of uniform angular width in elevation and having a uniform angular center-to-center beam spacing in elevation, said class of lower beam elements consisting of at least one element for producing one beam, each element of said class of lower beam elements being operable to produce a beam having a reduced angular width in elevation which is a single predetermined fraction of the width of each of said beams from said upper beam elements, each beam from one of said lower elements having a center line angular spacing in elevation beneath the center line of the next higher beam which is generally reduced from the spacing between said beams from said upper elements in proportion to the reduced beam width, the peak energy radiated at the center lines of each of said beams from said upper elements being substantially uniform, the peak energy radiated at the center lines of each beam from said class of lower elements being proportional to the peak energy radiated in each beam from said class of upper elements, the proportion being an inverse function of the respective beam widths. 16. Apparatus as claimed in claim 15 wherein said means for switching carrier frequency energy in said sequence is operable to energize all elements of said class of upper beam elements the same number of times in each switching sequence and to energize each element of said class of lower beam elements by a number of times less than the number of energizing times for each of said upper beam elements and having an inverse proportional relationship to the peak energy radiated in each lower beam versus the peak energy radiated in each of said upper beams to thereby provide for substantially uniform signal radiation energy of all elevation radiation angles within the radiation pattern. Other info: Inventors: Toman, Donald J. (Pleasantville, NY, US) Application Number: 549946 Filing Date: 1975-02-14 Publication_date: 1976-07-20 Assignee: Tull Aviation Corporation (Armonk, NY) Primary Class(es): 342/408 342/398, 342/414 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Wilbur, Maynard R. Assistant Examiner: Berger, Richard E. Attorney: Ailes; Curtis |
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