GB588044A - Improvements in aerial arrays - Google Patents

Abstract

588,044. Aerials. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. Oct. 31, 1944, No. 21297. [Class 40 (v)] A number of dipoles forming a vertical broad band directive aerial array are connected in cascade by a series of transmission line links ; the characteristic impedance of any link is higher than that of the link or line that feeds it, more precisely the link impedance may be equal to the impedance it feeds. Fig. 3 (not shown) illustrates a simple 4-unit array of folded dipoles spaced half of the mean band wavelength apart, the links feeding one dipole from the immediately preceding one having impedances as specified above. In Fig. 4, the dipoles are connected in two series, alternate dipoles being connected by links. The dipoles may be either the simple type shown in Fig. 4 or the cage type of Fig. 2 in which width " w " and depth, " d " can be adjusted to give the best frequency response over the operating range ; in either case when the switches 5 are open, the dipoles are of the full-wave type and when they are shut the dipoles become half-wave operating, on a band of frequencies half those in the full- Wave case. The coverage of the array is thus increased by the choice of two frequency bands. In Fig. 4, the feeder links should be one Wavelength long at the mid-point of the lower frequency band and the separation of adjacent dipoles a quarter wavelength, link 13 may be two, and link 14 one, wavelength long. The links in this example are longer than the direct spacings and, if desired, they may be shortened by using series loading coils with the appropriate shunt capacitors, Fig. 5 (not shown). The arrays may be provided with reflectors consisting of a similar series of dipoles mounted a quarter wavelength behind the first series ; arrays with reflectors, however, only work for one frequency range, i.e. with switches 5 permanently open or permanently shut ; and the reflector spacing is arranged correctly for the mid-point of the range. The reflector dipoles may be unfed and terminated by their equivalent impedance, or connected by a separate series of links exactly similar to the first, but fed in phase quadrature, or each dipole of the reflector may be energized from the terminals of its associate main array dipole by means of a quarter wavelength link. To take into account the mutual inductance between the array and reflector dipoles, small adjustments in dipole length may be required. Fig. 7 (not shown) illustrates an experimental method of determining the adjustment for the last. type of reflector connection described above. The Provisional Specification states that in an array without reflectors and with switches 5 closed, the dipoles will operate in half and full wave modes simultaneously if desired.