GB1293612A - Improvements in or relating to wide-band omnidirectional antennas for very short wave working - Google Patents

Abstract

1293612 Aerials THOMSON-CSF 10 April 1970 [15 April 1969] 17269/70 Heading H4A A wide-band aerial comprises at least one stage of four dipole planar arrays, which are arranged in a square around a mast. Each array consists of at least one pair of full-wave radiator elements which are fed in phase by a supply line and which are backed by a plane reflector. Auxiliary devices, comprising at least two elongated metal rods which are perpendicular to the surface of the reflector, are provided for each pair of radiator elements, and are disposed symmetrically with respect to said pair of elements and to said supply line. The horizontal radiation pattern of the array is modified by the auxiliary devices so that the amplitudes at angles of 45 degrees to the broadside axis are substantially half the amplitude along said axis, and diminish rapidly at greater angles. In a first embodiment, each array comprises a conductive reflector 3, Fig. 2, carrying eight thick, shortened dipoles, of which four are shown, i.e. 41, 42; 51, 52; 61, 62; 71, 72. The distance between adjacent dipoles is #m/2 (Xm = mean operating wavelength) and their distance from the reflector 3 is #m/4. They are supplied in phase through two-wire lines comprising flat sections 8 and round sections 9. A first type of auxiliary radiator element comprises angled pieces of metal 10, 11 respectively fitted to the conductors of the feeder section 8. These are disposed symmetrically between the two dipoles of each pair, i.e. there are four for an array of eight dipoles. The dimensions h, l are each approximately #m/4, and the ends of the elements are not in contact with the reflector 3. A second type of auxiliary element comprises conductive supports 43, 44; 53, 54; 63, 64; 73, 74 of the dipoles 41, 42; 51, 52; 61, 62; 71, 72. Said supports are offset in relation to the centres of the dipoles, and the distance between a pair is of the order of γm/4. Four of the radiating units set in square formation around a mast-head and fed in phase with equal powers provide an omni-directional radiation pattern. More than one level of radiating units may be provided, and they may be mounted around an enlarged extension of the mast, to improve accessibility. In another embodiment, passive auxiliary radiator elements 12, 13; 14, 15, Fig. 3, extend upwardly from the reflector 3 between pairs of dipoles 41, 42; 51, 52 and 61, 62; 71, 72. The said auxiliary elements are of circular or rectangular cross-section. Their height is approximately #m/4 and the spacing between pairs is approximately equal to the overall length of a dipole.