Wide-beam horn feed for parabolic antennas

Abstract

Current-flow is suppressed on the outer surface of the horn except in a small endmost region. A reflector surrounds the horn, spaced rearwardly from the mouth. A choke used for the suppression blocks current-flow between the horn and the reflector. A high degree of uniformity of the radiation pattern over a wide forward angle is achieved.

What is claimed is: 
     
       1. A wide-beam directive radiator for feeding parabolic reflectors and like uses comprising: (a) an open-ended high-frequency conductive radiating horn, and coupling means therefor adapted for operation at a preselected frequency,   (b) a forwardly facing conducting surface reflector having its central portion surrounding the horn at a distance of from approximately one-quarter wavelength to approximately three-quarters wavelength rearwardly of the end thereof,   (c) and high-frequency insulating means between the external surface of the horn and the inner portion of the reflector for blocking high-frequency current flow therebetween at the operating frequency .Iadd.said high-frequency insulating means being spaced rearwardly from the open end of said horn to permit radiation from a limited region of the outer surface of the forward end of said horn.Iaddend..   
     
     
       2. The radiator of claim 1 wherein the high-frequency insulating means comprises a shorted quarter-wave choke. 
     
     
       3. The radiator of claim 2 wherein the choke comprises a tubular conductor surrounding the outer surface of the horn and conductively shorted thereto at the rearward end. 
     
     
       4. The radiator of claim .[.3.]. .Iadd.1 .Iaddend.wherein .[.the forward end of the tubular conductor is rearward of the end of the horn to permit radiation from the outer surface of only the forward end of the horn.]. .Iadd.said high-frequency insulating means is spaced rearwardly from the open end of said horn by less than a wavelength.Iaddend.. 
     
     
       5. The radiator of claim .[.4.]. .Iadd.3 .Iaddend.wherein the forward end of of the tubular conductor, the forward end of the horn, and the peripheral portion of the reflector are in approximate radial alignment. 
     
     
       6. The radiator of claim 1 wherein the reflector is an uninterrupted plane surface. 
     
     
       7. The radiator of claim 1 wherein the reflector has conducting portions extending longitudinally forward at the periphery to block side radiation. 
     
     
       8. The radiator of claim 1 including a conducting member having its outer edge approximately radially aligned with, and between, the peripheral portion of the horn and the edge of the reflector. 
     
     
       9. In a primary radiator for feeding of large-aperture parabolic reflectors and like uses having an open-ended high-frequency conductive radiating horn and coupling means therefor adapted for operation at a preselected frequency, the improved construction for wide-beam radiation comprising a quarter-wave radiation choke for such frequency on the outside wall of the horn, spaced rearwardly from the open end thereof by a distance greater than about one-eighth wavelength but less than a wavelength, the portion of the horn wall between the choke and the open end being exposed for re-radiation.Iadd., and a conductive reflector extending transversely outward from said horn and spaced rearwardly from the open end thereof for reflecting forwardly a portion of the back radiation from the end of the horn, said reflector being isolated from the end of the horn by said choke.Iaddend..   
     
     
       10. The improved primary radiator of claim 9 having a conductive reflector extending transversely outward at a distance of from approximately one-quarter wavelength to approximately three-quarters wavelength rearwardly of the end of the horn and isolated from the end of the horn by the choke with respect to conductive current flow at the operating frequency, the reflector reflecting forwardly a portion of the back radiation from the end of the horn. 
     
     
       11. The improved primary radiator of claim 10 wherein the reflector is of transverse dimensions of approximately 1 to 5 wavelengths. 
     
     
       12. The improved primary radiator of claim 10 wherein the choke is approximately a quarter-wavelength from the end of the horn and the reflector is a radially extending planar conductor approximately a half-wavelength from the end of the horn.