GB1026558A - Improvements in log periodic antennas - Google Patents

Abstract

1,026,558. Aerials. GRANGER ASSOCIATES. Oct. 1, 1963 [Oct. 7, 1962], No. 38666/63. Heading H4A. A "log-periodic" aerial comprises two feeders extending from a ground point in a common vertical plane to a single tower, each feeder has linear and conductive radiating elements extending from it at intervals alternately to one side and the other side of the vertical plane, the lengths and spacings of the elements increase logarithmically from an apex at the ground point in accordance with where L N and L N+1 are the lengths of the Nth element and the element next nearest the apex, X N and X N+1 are the distances from the apex of the Nth element and the element next nearest the apex, and # is a constant less than unity, and the elements extend from the feeders in such directions that the angle #N, between a plane including the Nth element and its feeder, and the above common vertical plane, is other than 90 degrees. In one embodiment, Figs. 4, 4B, 4C the aerial elements 14, 15 are anchored to the ground by guy wires 21 and the feeders 11, 12 are supported from a mast 18 by a catenary 19. In an example, the operating frequency range is 4 to 30 Mc/s., the mast is transportable and 70 ft. high and # N is 125 degrees. The angle #, Fig. 4A is 90 degrees. Polarization of the radiation is horizontal, the longest element is #/2 long at the low-frequency end of the desired range and the shortest element is #/2 long at the high-frequency end thereof. The ensuing radiation patterns are discussed. The mast may be telescopic, or be composed of readily-connectable aluminium sections. Coiled guy wires are pre-assembled. The feeder and radiator assembly may be pre-assembled from flexible conductors and packed in a coil, the feeders containing a calibrated spring-tensioning device for rapid tensioning of the caternary. Ends of radiators, supported by insulating rope, may be fitted with snap hooks and means for rapid length and tension adjustments. Feeders 11, 12 may or may not be parallel. In another embodiment, Fig. 5, omnidirectional in azimuth, angle # is greater than 90 degrees, and a single central tower 22 supports four sets of pairs of feeders with dependent radiating elements.