GB1393160A - Travelling wave chain antenna - Google Patents

Abstract

1393160 Aerials M E TIURI 27 Sept 1972 [1 Oct 1971] 44575/72 Heading H4A A travelling wave aerial comprises a chain 1, Figs. 1, 2, of four sided links 3 connected together by parts 6, a ground plane 2 thereunder, and a feed cable with two conductors which are respectively connected to one end 7 of the chain 1, and to the ground plane 2. The connection parts 6 extend between the centres of adjacent long sides 4 of the links 3 and, as seen in plan view, are parallel to the short sides 5 thereof. The aerial is operable over a wide band of frequencies with low side lobes, the main beam having a elevation angle # which is frequency dependent. The far end 7 of the chain 1 may be left open, when radiation absorbing material may be installed thereunder, or it may be connected to the ground plane 2 through a suitable load impedance. It is also possible to feed the aerial at both ends, at different frequencies. The cross-sectional dimensions of the links and of the connection parts may be made to differ, so as to improve matching, for example, so that the characteristic impedance of the transmission line formed by a connection part 6 and the ground plane 2 is half the characteristic impedance of the transmission line formed by each half of a link 3 and the ground plane 2. The lengths of the sides 4 may be #, the lengths of the sides 5 and of the connection parts 6 may be #/4 to 3#/4, and the chain 1 may be #/10 above the ground plane 2, where # is the wavelength at the mean operating frequency. Instead of being rectangular, the links may be parallelograms, with their longer sides inclined to the connection parts (Fig. 3, not shown). The chain or the ground plane, or both, may be curved. The distance between the chain and the ground plane may increase from the feed end continuously or in steps, for example, from #/20 to 3#/10. The lengths of the sides of the links, and of the connection parts, may increase continuously along the chain, for example, by 2% from link to link, or two different sizes of connection part and link may be used alternately (Figs. 5, 6, not shown). In other arrangements, two such chains may be disposed side-by-side above a common ground plane, with adjacent shorter sides of links connected together, either at the ends thereof or along their entire lengths. The two chains are paralleled at their feed ends to a common source (Figs. 7, 8, not shown). An arrangement which provides elliptically or circularly polarized radiation comprises two angularly disposed aerials using parallelogramshaped links and having mirror-image symmetry about an axis 14, Fig. 9. A common feed point 9 is directly connected to one aerial, and is connected through a phase shift element 13 to the other aerial.