GB842063A - Omnidirectional beacon antenna - Google Patents

Abstract

842,063. Directive radio systems. STANDARD TELEPHONES & CABLES Ltd. Aug. 15, 1958 [Aug. 19, 1957], No. 26295/58. Class 40(7). The invention relates to an aerial system for a "TACAN" radio beacon and provides an aerial system of smaller size that those of the prior art whilst retaining a satisfactory fieldstrength pattern. In particular the pattern in the vertical plan has a maximum just above the horizontal, as is desired and then falls away substantially evenly as the elevation angle increases up to an angle of the order of 60 degrees. The embodiments described are for the production of a rotating beacon radiation pattern with a single main lobe and nine equally spaced minor lobes superposed thereon. In a first embodiment the radiating element 1 in the centre of the system is a cylindrical cup, quarter of a wavelength high, mounted over a central stationary part 6 of a ground plane. The element 1 is fed by a transmission line 12, 13. The rotating part of the system is mounted on a rotatable extension 7 of the ground plane capable of being driven by a motor 11. A choke joint 8, 9 is arranged between the two parts of the ground plane. Nine folded unipoles 2 are provided on the plane 7 equally spaced round the element 1 and each is fed by, and matched to, a transmission line 3 leading radially inward to a vertical pick-up element 16. The upper ends of the elements 16 are connected by a ring 17 supported on a dielectric cylinder 18. The folded unipoles are thus fed indirectly from the same source as element 1. Also included in the rotating structure are the nine parasitic elements 4 for the production of the minor lobes and a single inner parasitic element 4a mounted on the cylinder 18 which produces the major lobe. An explanation of the theory of operation of the folded unipoles in conjunction with the centre element is given and refers to Figs. 5 to 9 (all not shown). Fig. 4 shows a section, similar to that of Fig. 2, through another embodiment in which the central element is a dipole 19, 20 and all the elements are spaced above rotatable ground plane 33. The ground plane carries a dielectric cylinder 31 which supports inner parasitic element 32 and also nine radially arranged and equi-angularly spaced supports 30 each bearing in printed circuit form an outer parasitic element 25 and a folded dipole 24, coupled to a balanced pickup element 27 by a transmission line 26. The outer ends of the pick-up elements are coupled by upper and lower conductive rings 28 and 29 mounted on the dielectric cylinder 31.