GB538036A - Antenna systems - Google Patents

Abstract

538,036. Aerials ; directive wireless systems. STANDARD TELEPHONES & CABLES, Ltd. March 5, 1940, No. 4095. Convention date, April 26, 1939. [Class 40 (v)] [Also in Group XXXVI] A radio antenna in the form of a plane loop of small dimensions compared with the operating wave length is connected to a transmission line section which tunes the antenna and causes the current distribution in the loop to be substantially uniform, whereby radiant action is substantially uniform in all directions and the radiated waves are polarized parallel to the plane of the loop. The antenna is particularly intended for the radiation of horizontallypolarized waves, and for radio beacons. As shown in Fig. 1, the aerial comprises two conductors each a half-wave long, and with their centre portions bent to form a loop, the conductors having one end free, and the other connected to the transmitter or receiver 41. The current distribution as shown by the shaded areas, is such that radiation by the end portions is neutralized, whilst currents of substantially the same intensity throughout flow round the central loop portion, with the result that the radiation or reception is substantially confined to waves polarized in the plane of the loop. The end portions may be bent into a direction perpendicular to the plane of the loop, and may be enclosed in grounded shields, Fig. 2 (not shown), One half of the loop.may be omitted if a conducting sheet is placed so that that half is constituted as an image, Fig. 3 (not shown). Fig. 4 shows a modification in which four conductors 73 ... 76 forming a square are connected to a source 70 by parallel conductors occupying one diagonal, whilst the free ends lie in the other diagonal. One of the connections to the source is crossed over at 77 to give correct phasing, and to produce a current flowing round the loop. The aerial may comprise tubular radiators arranged as a square or circular formation supported at the top of a mast by four inclined tubes which shield the leads 71, 72 from the source and the free ends 731 ... 761 of the aerial, Figs. 5-7 (not shown). In a further arrangement, the inclined tubes are dispensed with (Figs. 19, 20 not shown). The aerial may comprise eight radiators forming an octagon, some of them being directly energized by the source 1100, Fig. 8, whilst others are coupled indirectly by their adjacent free ends. These couplings may be replaced by condensers, Fig. 8A (not shown), which may take the form of strain insulators. In Fig. 11 a loop 1301 arranged for reception on two wave-lengths is tuned by an adjustable metal plate 1305 and is connected through a loaded line 1307 to two shielded conductors 1308, 1309 of which the former 1308 is half a wave length long and is coupled by a concentric line 1310 to the receiver f 2 for that wave length, while the latter 1309 is coupled through a shielded pair transmission line 1311 to the receiver f 1 for the second wave-length. The arms of the loop 1301 may be broken up by condensers of small capacity, which may be formed as shown in Fig. 13 by a central aluminium rod 1504 projecting through an insulating block 1503 connecting two tubular sections 1501, 1502 of the loop. Owing to the absence of vertically-polarized components, the loops are suitable for use in guiding or runway-localizer beacons. Two loops 1701, 2 Fig. 15 placed half a wave-length apart are energized in phase opposition by a carrier source 1710 modulated at 1711 by a frequency F1, and are energized in phase agreement from the same source modulated at a frequency F2. A two-wire bridge network 1704 is employed for interconnecting the antennµ and the source, the arms of which are of length 15 of a wavelength. The polar diagrams for the modulations F1, F2 are shown in Fig. 16, giving four separate equi-signal guiding lines at about 60 degrees to each other. In another beacon arrangement (Figs. 17 and 18, not shown) four antennae are used in line, the carrier of modulation frequency Fl being applied to the outer pair in phase opposition and to the inner pair in phase with each other but in quadrature with the outer pair. The phases for the outer pair are interchanged for the carrier bearing the modulation frequency F2. The spacing of the outer pair may be 340 electrical degrees, and of the inner pair 160 degrees.