GB623556A - Improvements in or relating to antenna systems - Google Patents

Abstract

623,556. Directive radio systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 21, 1946, No. 15428. Convention date, Jan. 20, 1945. [Class 40 (vii)] In a broad-band directive aerial array comprising two colinear dipoles 1 and 3 spaced by 2/3#, the two dipoles are energized in phase quadrature from a single feed point, whereby the reactance of one dipole at frequencies differing from the resonant frequency is balanced out by the reactance of the other dipole and the array presents a substantially constant resistive impedance over a broad band of frequencies, e.g. a frequency range of 2: 1; a shield 9 is also provided between the dipoles to minimize coupling and the array is backed by a plane or parabolic reflector 5 provided with side members 7. As shown, each dipole, e.g. 1, comprises two cylindrical elements 11 and 13 secured to a tubular support 15 which has a #/4 slot 17 and the dipole is fed by a coaxial line 19 which has its outer conductor connected to the support 15 and its inner conductor extending up within the slotted portion of the support 15 and connected to the junction of the radiator element 11 with the support 15. The two dipoles are energized in phase quadrature by means of a branched coaxial line, the two branches 19 and 21 differing in length by #/4 and being matched to the main line 25 by a cascaded #/4 line transformer 27, 29. The directivity of such a system is unsymmetrical with respect to the normal to the line of the dipoles, Fig. 3 (not shown), and a symmetrical directivity may be obtained by displacing the dipoles 1 and 3 together with their associated reflectors in the direction of the normal, Fig. 4.