GB840444A - Antenna unit - Google Patents

Abstract

840,444. Directive radio systems. STANDARD TELEPHONES & CABLES Ltd. Aug. 30, 1957 [Aug. 31, 1956], No. 27408/57. Class 40 (7). An aerial system having a rotatable directive polar diagram consists of a vertically - disposed antenna, such as the fat dipole 1, capable of radiating vertically-polarized waves, and a plurality of vertical conductive strips 8 arranged coaxially round the antenna, each strip being in at least two portions (as shown in three portions 9, 10 and 11, separated by aligned gaps 15 and 16). Coupling- means rotatable around the antenna in the vicinity of the gaps are provided to capacitively couple together the portions of one or more of the conductive strips to form a reflector element or elements. The coupling means shown consist of the rotatable insulating discs 13 and 14 attached to the outside of radiation transparent tube 12 surrounding the antenna 1 and rotated by motor 19. Each disc carries a conductive peripheral member, 17 or 18, and a counterbalance weight 22. The members 17 and 18 capacitively couple together the portions of the strips against which they lie to form a group of parallel reflecting strips and the centre lengths 10 of the strips elsewhere round the antenna are chosen to be of such length that they act as directors. If the members 17 and 18 extend 120 degrees round the antenna a sharp single lobe directive pattern results (Fig. 3, not shown). It is also possible to use more than one member 17, 18, on each disc 13 and 14. For example, if two, each extending over 30 degrees and separated by 30 degrees, are used a twin-lobed pattern is obtained (Fig. 4, not shown) whilst three, arranged to extend over about 120 degrees in all, including the gaps between them, will give a three-lobed pattern (Fig. 5, not shown). Where a plurality of conductive members are used on each disc it is preferred to couple them by inductances (Fig. 2A, not shown). The strips 8 are preferably mounted on a stationary cylinder 7 of ceramic or fibre-glass material and may conveniently be stripes of silver material fixed on a ceramic cylinder at regular intervals. The fat-dipole, capable of wide-band reception, is provided with a central coaxial feeder 2 led out through cylinder 12 and motor 19. If the aerial system is to be used for direction-finding purposes the feeder 2 is connected to a receiver and amplifier 26 feeding the rotor coil 25 of a phase-meter 24 through a highimpedance transformer 27. The stator coils 23 of the phase-meter are energized with reference signals from an alternator 21 driven by motor 19 in synchronism with the aerial rotation. Specification 772,120 is referred to.