GB606926A - Improvements in directive antenna systems - Google Patents

Abstract

606,926. Directive radio systems. WESTERN ELECTRIC CO., Inc. Jan. 22, 1946, No. 2085. Convention date, Jan. 24, 1945. [Class 40 (vii)] A directive aerial system comprises a concave reflector with a primary aerial mounted near the focus and a deflector extending parallel to the axis of the reflector and located between the primary aerial and the reflector whereby the shadow effect of the primary aerial is reduced. The invention is described as an improvement on that disclosed in Specification 574,610, which shows a switched overlapping-lobe aerial suitable for a radar system comprising a concave reflector formed as a surface of revolution about a horizontal axis 14 and a pair of vertical wave-guides 3 and 4 extending partly across the reflector with radiating apertures 6 and 7 facing the reflector. The apertures are covered by a double polystyrene window 8 and are connected to a transceiver 1 through a switch 5 which renders the guides alternately operative. In such a system, secondary lobes of appreciable magnitude are formed due to the shadow effect of the waveguide feed and in order to reduce this effect a small horizontal flat metallic deflector plate 9 with a circular front edge extending outwardly a distance of #/2 is attached to the wave-guides just below the apertures so that most of the energy radiated downwards from the apertures, e.g. along directions 31 and 32, Fig. 1, is deflected towards the upper portion of the reflector, the radiation reflected by that portion of the reflector facing the wave-guide feed being then reduced. Preferably, the reflector comprises two sections, the upper paraboloidal section 12 being formed by revolving the parabola 18, Fig. 1, about the axis 14 and the section being cut so that the horizontal dimension of the aperture is greater than the vertical giving a curved aperture of elliptical shape, Figs. 2 and 3, which produces a fan-beam which is highly directive in the horizontal plane and less directive in the vertical plane. The lower section 13 is conical shaped; alternatively, it may be barrel-shaped being formed by revolving the bottom edge 19, Fig. 1, of the paraboloid through a small angle about the axis 16, Fig. 2, or it may comprise an extension of the paraboloid 12. The reflector extends above and below the axis 14 distances B and A respectively and B is preferably equal to twice A so that the plane of the aperture 22 is inclined to the vertical. The lower section of the reflector is a continuous surface, but the upper section is a grille composed of horizontal metallic strips 23 having a depth D, Fig. 1, and vertical spacing V, Fig. 2, of about one inch corresponding to less than #/2 at the operating wavelength of 9.8 cms. The strips are supported by transverse members 25 and a rim member 26 which may be of conductive or non-conductive material since the reflector is designed for use with horizontally polarized waves which are not affected by the vertical transverse members. Figs. 5 and 6 (not shown) illustrate the improved horizontal and vertical polar diagrams produced by the arrangement of the present invention compared with that produced by the arrangement disclosed in Specification 574,610, Fig. 4 (not shown).