GB649944A - Improvements in and relating to radio aerials - Google Patents

Abstract

649,944. Aerials. BRITISH BROADCASTING CORPORATION, PAGE, H., and MARTIN, J. E. April 12, 1948, No. 10146. [Class 40 (vii)] A radio antenna comprises two co-operating members, at least one of which is frusto-conical (or like flaring shape) and is coaxial with, and surrounding, a conductive support, a conductor extending from inside the support providing a connection to the smaller end of the cone member and a conductive screen extending between the inner surface of the cone and the support arranged to reduce unwanted radiation from the space between the inside of the cone and the support. Fig. 2 shows such an antenna in which each member is frusto-conical and fed at the smaller end by paralleled wires attached to one of the feeders passing down support 12. Screens 17 comprise flat discs attached to the inside of the cones and to the support. They may serve mechanically to support the cone members and are so placed that the slant height " h from the top of the cone to them is a quarter of the operating wavelength. The screen shape may be varied, for example the screen may comprise a cylinder extending inwardly from the narrow end of the conical member (as shown at 18, Fig. 6) for a distance of a quarter of the wavelength and then being closed to the support. In another example (Fig. 4, not shown), the screen is frusto-conical, coaxial with the support, and attached to it in the plane of the conical antenna member's smaller end. The flare angle is made the same as that of the antenna member, the slant height a quarter wavelength and the larger diameter end is connected continuously to the antenna member. To decrease the weight and windage of the conical members the conical portion beyond a slant height of one wavelength may be continued by a system of conical wires. Such an antenna besides including a screen or screens as previously described may also have additional features to prevent the undesired field inside the cone, such as the tapering of the conductive surface to the point of connection of each of the wires, Fig. 6 (also Fig. 5, not shown) and the insertion of a second screen 22. The screen 22 of frusto-conical shape and slant height of a quarter of a wavelength is attached inside the antenna cone 11 by a continuous member at its narrow end and placed so that the larger end is substantially coplanar with the larger end of the complete cone surface. An antenna having a single frusto-conical member and in which the second member is a flat sheet at right angles to the support and mounted close to the narrow end of the conical member is described with reference to Fig. 7 (not shown).