GB559886A - Antenna systems - Google Patents

Abstract

559,886. Wireless aerials. STANDARD TELEPHONES & CABLES, Ltd. June 26, 1942, No. 8821. Convention date, July 2, 1941. [Class 40 (v)] In a Vee or double Vee (rhombic) antenna comprising angularly related conductors the diameter of each conductor increases from one end to a maximum at a point intermediate the ends, and decreases from this point to the other end, the surge impedance varying smoothly along the conductors. The antenna has low reflection losses, the conductors are of sufficiently small diameter at their widely-separated ends for conveniently coupling them to similar conductors to form a rhombic antenna, and the input impedance may be matched to that of the line. The surge impedance may vary along the antenna according to an exponential law. In one form multiwave conductors are used, the diameter or width of which at any point is such that the surge impedance varies exponentially from a small value at the ends connected to the line up to a greater value at the widely separated ends. Fig. 1 shows a horizontal double Vee antenna the conductors 4, 5 of which consist of uniform wires carried by annular spacers 15 so as to form cage elements of circular section and now uniform diameter. The conductors are supported by insulators 6 and their rear ends are connected respectively by a line 10 to a translation device 11 and to a terminating impedance 12. The wires may alternatively be carried on spreaders to form a flat grid the plane of which is perpendicular to that of the antenna, whilst the width at any point is substantially the same as the diameter of the corresponding cage conductor. The method of calculating the variable diameter of the conductor to obtain a suitable exponential impedance variation is described. The curve 23, Fig. 5, shows the result for an antenna in which the conductors are 62 feet above ground, 315 feet long, are at an angle of 28 degrees to each other, and have an arbitrary selected diameter of 3 inches at their widelyseparated ends. The surge impedance at the terminals of the line 10, to match that of the line, is assumed to be 600 ohms, and that at the widely-separated ends 3 of the conductors is calculated to be 715 ohms using the above data. The exponential taper index necessary to produce the change from 600 to 715 ohms is then calculated, and from this the effective diameter of the conductor at each point is determined. In Fig. 5 the curve 23 exhibits the relation between the conductor radius and the ratio S/2H, where S= the separation of the two conductors at any part of the Vee and H= the height of the conductors above ground, the maximum radius occurring at a point corresponding approximately to S/2H= 0.7. A horizontal scale of surge impedance is also given, and the points 24, 25 on the curve 23 indicate two positions on a conductor where the diameters are the same but the surge impedances are different. A formula is given for calculating the actual diameter of the conductor from the effective diameter, as above found, the former being somewhat greater. The conductors may be solid, instead of being formed by spaced wires. Specifications 353,517, 392,201, and U.S.A. Specification 1,950,407 are referred to.