GB487708A - Improvements in or relating to aerial and feeder systems - Google Patents

Abstract

487,708. Aerial; directive wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. March 19, 1937, No. 8116. Convention date, April 28, 1936. [Class 40 (v)] An antenna system comprises a pair of halfwavelength conductors making an angle of 60‹ with each other and excited so that they have opposite instantaneous polarities at corresponding points. In a modified arrangement three half-wavelength conductors are arranged in an equilateral triangle and excited so that adjacent ends have opposite instantaneous polarities. Several arrays are described involving two or more such triangles and means are provided for matching the feeders with the radiators and with the main transmission line. Fig. 4 shows triangular systems fed by a series circuit. Alternatively the three feeder pairs may be fed in parallel. The feeder pairs terminate at their lower ends in half-wavelength loops A<1>, B<1>, C<1> and the point at which the transmission line is connected to a loop is chosen to match the line to the feeder system. Similar loops A<11>, B<11>, C<11>, A<111>, B<111>, C<111> may be provided as shown in Fig. 5 for matching the feeders to the radiating wires. In the arrangement shown in Fig. 4, in which the sets are half a wavelength apart vertically, corresponding ends of successive radiating wires are connected to different ones of a pair of feeder wires. They may be connected to the same feeder by spacing them one wavelength apart or, as shown in Fig. 6, by arranging cross connections 17 at each side of transverse metallic spacers connected conductively to the feeders at voltage nodes. In another arrangement, Fig. 7 (not shown), the radiating conductors are fed at points between their ends chosen from the point of view of impedance matching. Because of the abrupt change in load impedance as the feeders pass the level of each radiating system, corresponding abrupt changes may be made in the dimensions of the feeders. Adjacent feeders of the same or different pairs may be connected together at the top by loops which act as inductances and so modify to some extent the natural frequency of the radiating conductors. In a further modification, Fig. 10, braces are arranged as shown at each level, the bracing members being welded, riveted or otherwise rigidly secured together at their intersections. There may be secured at these points of intersection, which are points of zero potential, further feeders for other antenna systems, observation instruments, &c. Only the middle triangle is fed directly from the transmission line 46, the connection being effected by coaxial feeders, the outer conductors of which serve to couple the middle with the lower triangle. The upper triangle is similarly coupled by extensions of the outer conductors. For impedance matching reasons, for the last quarter wavelength, the ratio of the diameters of the outer and inner conductors of the coaxial feeders is increased. For a similar reason, the feeders are fed from the main transmission line 46 in series instead of in parallel, appropriate phase relations between the feeders of a pair being obtained by means of U-shaped sections 37, 42, 43. The paired feeders are fed by three single feeders 40, 44, 45, the shell of 40 being connected to the core of 44 and so on. Two of the three feeders are surrounded by a shell 47 for a quarter-wavelength. The paired feeders may feed the same radiating conductor or different ones. Fig. 12 shows a matching circuit for associating separate push-pull transmitters, e.g. for sound and television. The filter system shown in the rectangle 53 is for preventing energy from one transmitter from entering the circuits of the other and forms no part of the invention. The coaxial pairs 63, 64 from one transmitter are associated with the main line by connecting the separate cores to the shell and core respectively of a quarter wavelength coaxial line 61 connected to the main line, and connecting the shells of the separate pairs 63, 64 to a quarter-wavelength sleeve surrounding the line 61. Both inner and outer conductors of the section connecting 61 to the filter may be tapered so as to give a neat appearance while keeping the diametrical ratios of the conductor, and therefore the surge impedance, constant.