GB1254995A - Backlobe reduction in reflector-type antennas - Google Patents

Abstract

1,254,995. Aerials. ANDREW CORP. 23 Jan., 1970 [29 Jan., 1969], No. 3321/70. Heading H4A. A main reflector of a microwave aerial has on its edge an extension which departs in shape from the reflecting surface, and which comprises means for producing progressive advances and retardations of phase, within a range exceeding 180 degrees, of rearwardly diffracted radiation fields. The interaction of the variously phased fields results in wide directional diffusion of the diffracted energy. As described, a crosspolarized aerial 10 comprises a circular parabolic reflector 12 and a feed assembly 14. The periphery of the reflector 12 is provided with a welded-on rim 42 formed from angle-stpck, the radially-extending web of which constitutes a twelve-sided diffraction ring 46 around said reflector. Each side of the ring comprises a tangential portion 48 and short flat portions 50. The maximum radial extension of the ring 46 is approximately equal to the wavelength at the operating frequency of the aerial. The reflector 12 is made of aluminium and is provided with a rearwardly extending flange 38. A reinforcement ring 40 is welded to the main body of the reflector 12 and to the flange 38. A matching vertex plate 22 is provided in the centre of the reflector, and through this extend two waveguides 18, 20 to a dual-polarized horn feed 16. Said feed, which is of the kind described in Specification 1,199,226, comprises a square horn surrounded by a square sleeve, a circular intermediate vane, and a circular shielding skirt, which are mounted on a round reflector plate set back from the mouth of the horn (Figs. 5, 7, not shown).