Wide-Beam Horn Feed for Parabolic Antennas

摘要

1,199,226. Aerials. ANDREW CORP. 17 May, 1968 [25 May, 1967], No. 23510/68. Heading H4A. An open-ended radio feed horn is provided on its outside wall with a quarter-wave choke (the wavelength being taken at a preselected midband frequency) the forward end of which is rearwardly spaced from the open end of the horn by a distance greater than one-eighth of a wavelength but less than a wavelength. As described, a circular waveguide 10, Figs. 1, 2, has an open radiating mouth 14. A sleeve 16 of larger diameter than the waveguide is backwardly offset from the mouth 14 and is mounted on a support ring 18. The annular region between the sleeve 16 and the outer surface of the waveguide is dimensioned to act as a quarter-wavelength choke at the frequency of operation. An annular reflector plate 22 surrounds the outer surface of the sleeve 16 and is secured by a second support ring 24. The other end of the waveguide 10 is provided with a flange coupling 12. In a second embodiment (Fig. 6, not shown), a circular waveguide terminates in a radiation-transparent window, the edges of which are clamped between a flange formed on the outside of the waveguide, and a clamping ring. A quarter-wave choke sleeve and a reflector plate are provided which are backwardly offset from the radiating mouth of waveguide, and the said reflector plate has additionally a shield or skirt extending forwardly from its edge. In a third embodiment (Fig. 7, not shown) a rectangular waveguide is used. The reflector plate may be rectangular or circular and carries the quarter-wave choke sleeve surrounding the mouth of the waveguide and conforms in shape thereto. A series of forwardly projecting parallel vanes is provided at the edges of the reflector plate which are perpendicular to the electric field orientation of the fundamental mode in the rectangular waveguide, and which extend for substantially a quarterwavelength, so defining a series of chokes. Where the waveguide is to handle crosspolarized signals, the vane structure is extended along all margins of the reflector plate. In a fourth embodiment (Fig. 8, not shown), a flared radiating horn is provided at the open end of the waveguide and is surrounded by a correspondingly flared choke sleeve.