Patent GB-610517-A (GB)
Title: Directive antenna of variable directivity
IPC: G01S13/42
Filed: 1945-05-30
Abstract: 610,517. Directive radio systems; keying carrier frequencies. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 30, 1945, No. 13620. Convention date, June 30, 1943. [Classes 40 (v) and 40 (vii)] [Also in Group XXXVII] An antenna system comprises a radiator system which may be energized in a plurality of different modes so that a different beam deflected from the mean axis of the system is radiated for each mode and a plurality of transmission lines, one for each mode of energization, arranged to be coupled successively to an associated transmitter so that the resultant radio beam is successively directed into the four quadrants of a circle perpendicular to the mean axis. A sheet radiator 30, Fig. 2, mounted in a paraboloidal reflector which may be of open mesh construction and mounted over the face of a searchlight with the mean axis aligned with the light beam, is isolated from the surrounding sheet 33 by a quarter-wavelength deep channel 32, and may be energized at the mid-point of any one of its sides by one of conductors 35, 37, 39, 40. The radiation lobe is deflected about a line perpendicular to the plate towards whichever side of the plate is energized. In order to feed the energization successively to the four conductors. 35, 37, 39, 40, these being inner conductors of concentric lines 15, 19, a keying device such as is shown in Fig; 4 may be used. Only parts associated with lines 15 and 19 are illustrated in this Figure, the other parts at right angles not being shown. Concentric line 24 from the transmitter is connected by quarter - wavelength lines to the junction, e.g. 55, of lines 15, 19, &c., and their respective closed full-wave traps 45, 49. Considering the connection to line 19, point 55 is a quarter-wavelength from one end of trap 49 and at point 56 a quarter-wavelength from the other end a plate 57 extends inwards within a common cylindrical housing 58. Two parallel plates 59 mounted on a spindle extension 60, driven by motor 23 but electrically isolated by trap 61, rotate within the housing and when they cover one of the plates, such as 57, a high impedance is presented at points 56 and also 55 and energy flows into line 19. If, however, plates 59 do not cover plate 57, a low impedance is presented at 56 and 55 and a high impedance at the input to line 19 and so no energy flows to line 19. Spark gaps 62 are provided between plates 57 and 59 to encourage continuous sparking. In the above arrangement the plane of polarization of the transmission varies according to the side of the radiator being used. Fig. 5 shows a system in which the plane of polarization is always the same. Feed lines 92 and 93 are connected to the midpoints of opposite sides of the sheet, but lines 77 and 87 are split so as to feed the sheet in push-pull at points 70, 71, 'and 80, 81 near adjacent corners. An ordinary distributor 102 with rotary arm 103 connects the transmitter 26 to the antenna feeders. The antennµ may be used, for example, for pulse radar, with one pulse radiated for each change of direction. In such a system any echo pulses are received before, in the case of the first embodiment, the switch changes to the next position and a T-R box is used to separate the transmitter and receiver connections. In Fig. 5 the receiver 27 is connected to the sheet by pushpull feeders 104, 105 attached to the centre of opposite sides and thus receives over a central undetected pattern. Spark gaps 125, 126, at the end of quarter-wave lines 106, 107, break down to prevent direct connection between receiver and transmitter. The received echo pulses may be displayed in pairs for comparison on a cathode-ray oscillograph. A different type of keying switch, Fig. 6 (not shown), has the transmitter feeder divided into four quarter wavelength branches, each matched to a quarter-wave resonant line section, closed at one end. The four radiator transmission lines are also matched into these resonant lines which are arranged symmetrically with their open ends under a circular motor driven plate having one hole which passes over each resonant line in turn, thereby allowing energy to flow in the feeder connected thereto. In a further embodiment, Fig. 8, four half-wave radiating elements, one for each quadrant are mounted on insulators and provided with slidable turning sleeves; only two opposing radiators 200 and 202 are shown in the Figure. The radiators have their ends 211 arranged opposite energizing rods 214 and 216; a disc 223, with a single aperture 224, driven by motor 23, allows each radiator to be energized by its respective rod in turn. All the energizing rods are fed continuously from co-axial line 24.