GB1000855A - Improvements in or relating to electromagnetic wave transmitting aerials - Google Patents

Abstract

1,000,855. Aerials. SIEMENS & HALSKE A.G. Aug. 15, 1963 [Aug. 17, 1962], No. 32282/63. Heading H4A. The effects of reflections from a radome surrounding an aerial array are minimized by spacing the elements of the array at distances from the radome such that the reflections mutually cancel at a junction in the feeder, supplying the elements. As shown in Fig. 1 an omnidirectional aerial comprises two vertically stacked units 1, 2, each containing two vertical arrays of eight parallel horizontal dipoles 7-14, each array being backed by a respective reflector 5, 4 and the two arrays being directed in opposite azimuthal directions. In further embodiments more than two arrays may be employed, arranged such that the dipoles in horizontal planes of the aerial lie along the sides of a polygon. The arrays are surrounded by a barrel-like radome 6 shaped so that the difference in diameter between the ends and the mid-plane is #/2 (where # is the mean operating wavelength). In this way the reflections from the radome to two adjacent dipoles in each array arrive in different phases so that they tend to cancel at a junction 15, Fig. 2, in the cophasal feed to the dipoles. In other embodiments, Figs. 3-5 (not shown), radomes of straight cylindrical form with the dipoles staggered therefrom, or radomes formed from two opposed frusto-conical sections, may be employed. In another embodiment, Fig. 6 (not shown) the dipoles are arranged horizontally around the sides of a rectangle whose centre is horizontally displaced by #2#/8 from the longitudinal axis of a cylindrical radome, along a diagonal of the rectangle. It is stated that the invention may be applied to existing aerials by suitably displacing the aerial elements and that the wall thickness of the radome may be varied along its length. The radome may be made of woven fibreglass.