CONICAL REFLECTOR ANTENNA

• US 3,623,114 A
• Filed: 08/11/1969
• Issued: 11/23/1971
• Est. Priority Date: 08/11/1969
• Status: Expired due to Term

• Current Assignee: Arthur F. Seaton, N/a,, Paine T O Administrator of The National Aeronautics and Space
• Original Assignee: Arthur F. Seaton, N/a,, Paine T O Administrator of The National Aeronautics and Space
• Inventors: Seaton, Arthur F., N/a,, Paine, T. O. Administrator of the National Aeronautics and Space
• Primary Examiner(s): Lieberman, Eli
• Application Number:
  US04/848,776
• Time in Patent Office: 834 Days
• Field of Search: 343/770,771,773-775,781,834,840,835,797,853,912
• US Class Current: 343/771
• CPC Class Codes: H01Q 19/15 the primary radiating source being a line source, e.g. leaky waveguide antennas
• CPC Class Codes: H01Q 25/02 providing sum and difference patterns H01Q25/04 takes precedence

Abstract

A conical reflector antenna is disclosed with a feed that is either a close approximation to a line source or a cylindrical structure which is electrically equivalent to a line source. Nearly complete control of its aperture illumination function is achieved by exciting various amounts of the line source or cylindrical feed. In addition to beamwidth control of a collimated beam that is linearly or circularly polarized, phasesensing monopulse operation is made possible by dividing a cylindrical feed structure into three equal sectors and incorporating conventional directional couplers for obtaining the difference between received signals from sectors on either side of a vertical axis for azimuth error, and the weighted difference between the sum of those signals and the signals from the third sector for an elevation error.

Claims

1. In a directional antenna having a conical reflector and a feed disposed inside said reflector along the axis thereof, an improvement in the feed comprising a plurality of radiating elements disposed about the axis of said reflector at various levels from a level near the apex of said reflector to a level closer to the aperture of said reflector at the end thereof opposite said apex, said elements being oriented to direct rays of radiant energy toward the inside surface of said reflector at an angle phi with said axis of said conical reflector as measured from the apex of said reflector, and said angle is substantially equal to 180* less twice the half-angle of said reflector as measured from said axis to the inside surface thereof, whereby collimation of said rays emanating from the aperture of said reflector is achieved, said elements at a given level being disposed about said axis in pairs, with elements of a given pair on opposite sides of said axis, said pairs being uniformly spaced about said axis and arranged to radiate with a progressive interelement rotation of 360*/n, where n is the number of said elements at said given level, thereby substantially reducing cross-polarization.

2. Apparatus as defined in claim 1 wherein all of said elements at said given level are excited in phase.

3. Apparatus as defined in claim 2 wherein each element radiates linearly polarized energy.

4. Apparatus as defined in claim 1 wherein each element radiates circularly polarized energy, and elements of a given level are arranged to radiate with a progressive interelement rotation of 360*/n by orienting each element in a like manner and feeding all elements of said given level in sequence around said axis with a progressive interelement phase shift of 360*/n, where n is as before the number of said elements at said given level.

5. Apparatus as defined in claim 1 wherein said feed system for a given level comprises a waveguide curved into a cylindrical form having as its axis said axis of said reflector and having slots as elements disposed about its axis for radiating energy

6. Apparatus as defined in claim 5 wherein said slot elements are disposed about said axis of said cylindrical form in pairs, with slot elements of a given pair on opposite sides of said axis, and said slot elements are uniformly spaced.

7. Apparatus as defined in claim 6 wherein each of said slot elements radiates circularly polarized energy, and all of said slot elements are oriented in like manner and fed with a progressive interelement phase shift of 360*/n, where n is the number of said elements at said given level.

8. Apparatus as defined in claim 7 wherein said progressive interelement phase shift is achieved by making the guide wavelength of said waveguide longer than required for inphase radiation.

9. Apparatus as defined in claim 8 wherein said levels are grouped in sections for separate and selective excitation to provide a desired beam width of rays emanating from the aperture of said cone.

10. Apparatus as defined in claim 1 including means for combining said elements into groups of adjacent elements to provide signals proportional to radiant energy received by said elements in groups, and means for deriving a first error signal proportional to the difference between signals provided by first and second ones of said groups of elements in adjacent sectors, whereby tracking said target in one plane is provided upon directing said antenna to reduce said first error signal to zero.

11. Apparatus as defined in claim 10 including means for deriving a second error signal proportional to the difference between signals provided by third and fourth ones of said groups of elements in adjacent sectors, whereby tracking said target in a second plane while tracking in said first plane is provided upon directing said antenna to reduce said second error to zero while directing it to reduce said first error signal to zero.

12. Apparatus as defined in claim 11 wherein said first and second ones of said groups of elements receive radiant energy from equal sectors, said third one of said groups of elements consists of said first and second ones of said groups of elements combined, and said fourth one of said groups of elements consists of all remaining ones of said elements not included in said third one of said groups.

13. Apparatus as defined in claim 12 wherein all sectors are of equal size, and said first and second tracking planes are perpendicular.