GB675101A - Improvements in or relating to aerials - Google Patents

Abstract

675,101. Aerials. NATIONAL RESEARCH DEVELOPMENT CORPORATION. May 11, 1950 [May 11, 1949], No. 12622/49. Class 40 (vii). A hollow conical dipole aerial comprises an upper frusto-conical element 4 which is mounted co-axially upon a cylindrical supporting mast 3 with a conical conducting screen 5 extending between the element 4 and the mast, and a lower frusto-conical element 1 which is supported upon the mast by a conducting annular member 2 closing the truncated end of the element 1. The aerial is fed by a parallel-wire feeder or, as shown, by a co-axial feeder 6 passing up the centre of the mast and emerging through a hole 7, one conductor being connected directly to the member 2 and the other being connected, preferably through a condenser 10, to the truncated end of the element 4. The screen 5 may act as a support for the element 4 or, alternatively, the screen may be constructed of thin metal, the element being supported by a further insulating member. A further support comprising a disc 11 of dielectric material may be provided. Also a cylindrical shield 12 of dielectric material may be provided. The position of the screen 5 is so chosen as to balance out the reactive component of the aerial impedance. The arrangement illustrated may be repeated at intervals up the mast to form an array; on account of the screens 5 negligible stray coupling exists between adjacent dipoles. The Provisional Specification also describes a conical dipole aerial having similar upper and lower elements, each having a screen extending from within the element to the mast. The distances of the screens from the mouths of their respective cones differ so as to increase the band-width of the aerial. An alternative arrangement comprises a step in the screen 5, thereby effectively creating in the upper cone two cavities of different dimensions and so increasing the band-width of the aerial. Reference has been directed by the Comptroller to Specification 649,944.