GB573436A - Improvements in directional short-wave aerials - Google Patents

Abstract

573,436. Aerials. GENERAL ELECTRIC CO., Ltd., and CLAYTON, R. J. Aug. 19, 1942, No. 11695. [Class 40 (v)] In a short-wave aerial comprising a central conductor 1 fed from one end 3 and surrounded at intervals by conducting cylinders 2 so as tc leave the conductor 1 exposed at intervals at least in one direction the conductor is covered by a sheath (not shown) of a thickness consider. ably greater than the diameter of the conductor and of a dielectric of a permittivity greater than that of the surrounding medium. When the surrounding medium is air, a suitable material for the sheath is poly. thenÚ or polystyrene and its thickness may be equal to the inner diameter of the cylinders 2 so that it serves as a support for these cylinders. The cylinders may be provided with end shields which may be tapered, Figs. 2a-2c (not shown). The spacing should be such that the distance between corresponding points of adjacent radiating sections of conductor 1 is approximately equal to the wave-length of propagation in the aerial. As shown, the lengths of the exposed and unexposed parts of conductor 1 are equal and the conductor is of uniform diameter, but in modifications (i) the length of the exposed part is reduced and that of the cylinders increased and the diameter of the conductor inside each cylinder for a quarterwave-length from the feed end is increased to decrease the characteristic impedance and maintain the current constant, or (ii) each unexposed part of the conductor is divided into two quarter-wave sections of different characteristic impedance, in which case the current decreases progressively from the feed end. To get a lateral directive effect, the exposed portions may be associated with V- shaped screens or a continuous cylinder may be used with spaced apertures at one side. Specifications 489,775 and 543,337 are referred to.