Patent GB-1230802-A (GB)
IPC: H01Q11/10
Filed: 1968-06-04
Abstract: 1,230,802. Aerials. GRANGER ASSOCIATES. 4 June, 1968 [23 June, 1967], No. 26446/68. Heading H4A. An aerial system comprises a generally horizontally disposed planar array-configuration of spaced radiating elements and a supporting construction, the outlines of the plan projections of the two being substantially co-extensive Each radiating element comprises a pair of elongated non-rigid members which are supported at their outer ends to diverge progressively towards their inner ends. As described, a log-periodic dipole array, in which the dipole arms 12, Fig. 10, consist of narrow Vees of stranded aluminium wire, is carried by a supporting assembly, having three booms 16, 17, 18, which is rotatably mounted on a support tower 10 by means of a four-point contact type ball-bearing (Figs. 8, 9, not shown). The booms 16, 17 include dielectric splices (Figs. 5, 6, 7, not shown) and all booms are braced by stays. Fibreglass catenary cables 19, 21 and 23, 24 are strung between a fibreglass tubing support 22, carried at the front end of the boom 18, and the ends of the booms 16, 17. These cables serve respectively to support dipole arms at their tips and intermediate their lengths (Fig. 3). The other ends of the Vees are secured to pivotally mounted spacer support arms 61, Fig. 12, and in each dipole the two support arms 61 are separated by an insulator bar 62. An arcuate support bracket 63 connects each dipole arm to one of two wires 37, 38 which run as a feed line along the length of the array and inside the boom 18. A four-wire return feed line is connected to the two-wire feed line at the front end of the array, and runs to the centre of the array. Inside the boom 18 the two feed lines are supported by means of insulating frames (Fig. 13, not shown). The two-wire feed line runs to the back radiator 12a, and is tensioned by a fibreglass cable 54 extending from the ends of the booms 16, 17. A parasitic element 43 may also be provided, located beyond the back radiator 12a. At the centre of the array the four-wire return feed line is extended down the middle of the support tower 10 towards ground level. The wires are secured to, and are insulated from the supporting assembly and also the bottom of the tower (Fig. 16, not shown). Insulating spacers are provided at intervals along the run of the feed line in the tower (Fig. 15, not shown). The wires are of flexible construction, for example, having a steel central portion and an outer conductive portion of aluminium, so that the array may be rotated by Œ 180 degrees, or more, by a drive motor (Fig. 17, not shown). Vane assemblies 51 may be carried at the ends of the booms 16, 17 which each comprise a number of parallel spacedapart aluminium tubes (Fig. 11, not shown). These are intended to provide aerodynamic balancing for the array and supporting assembly both in normal conditions and when there is ice formation. In the latter case ice formed between the spaced apart aluminium tubes of the vane assemblies provides compensation for the effects of ice upon the array and the supporting assembly. The catenary cables supporting the dipole arms at their tips may be omitted. In one such embodiment (Fig. 14, not shown) the Vee portion of a dipole arm which projects beyond the intermediate supporting catenary cable is housed in two hollow aluminium tubes secured to said cable. In another such embodiment (Fig. 18, not shown) the dipole arm shape is modified, its end portion being housed in a single hollow aluminium tube which is secured to the intermediate supporting catenary cable.