GB812398A - Directive aerial - Google Patents

Abstract

812,398. Aerials. HOLLANDSE SIGNAALAPPARATEN N.V. Aug. 7, 1956, No. 24178/56. Class 40 (7). The invention relates to a directive aerial system capable of giving a beam with a plurality of different scanning motions. In particular a radar aerial capable of radiating a conically scanning target position indicating beam and also a broader search beam is described. Such an aerial comprises a beam concentrating device in the form of a reflector 101, an eccentrically rotated waveguide nozzle 102 directed into the reflector and operative to provide the conical scan, and a second radiating system 105 situated between the eccentric nozzle and the reflector, mounted to provide at least one type of scanning, and comprising at least one radiating doublet and a reflector on the opposite side of it to the reflector 101. The reflector can itself be moved about vertical and horizontal axes and the waveguide nozzle system which may be of the type described in Specification 731,586 is supported by four isolating supports 103 and fed by waveguide 104. The radiation from the nozzle is such that the source appears to rotate about the focal point of the reflector and a sharp beam is produced. The second radiating system 105 consists of a doublet 202 carried by a strip of metal 203 supported in the tapered mouth of waveguide 201. An auxiliary reflector 204 is attached to the end of the strip and directs energy from the doublet into the reflector 101. The whole radiator is enclosed in a cover of lowloss dielectric. In variations the second radiating system may include more than one energized doublet, the reflector may be a reflector doublet, and a coaxial line feed instead of a waveguide feed may be used (Figs. 3 to 6, not shown). The feeder for the second radiator may be mounted so as to pivot or may be supported on a gimbal ring for movement about two orthogonal axes. Suitable joints will be necessary in each case for the waveguide or coaxial line feeder. Mechanical linkages capable of providing a linear or a two-dimensional scanning movement of the second radiating system are described with reference to Figs. 8 and 9 (both not shown) respectively. It is essential that when it is operative the radiation from the second radiating system should appear to come from a point which, during scanning, passes through the focus of the reflector. It is found possible to arrange for this without making the conical scan waveguide nozzle retractable. However, when the nozzle is in use and the second radiator inactive the presence of the second radiator between the nozzle and the reflector may cause the production of undesired side lobes in the radiation pattern. To prevent the occurrence of these, or to reduce them in amplitude, various precautions are suggested. Firstly the second radiator when not in use should be locked in an extreme position or even moved out to beyond an extreme scanning position. Secondly the second radiating system may be withdrawn towards the reflector when not in use. An arrangement in which the radiator is withdrawn by springs and forced into its operative position by compressed air pressure is described with reference to Fig. 7 (not shown). To prevent the doublet of the second radiator resonating when the nozzle feed is being used the two radiating systems should be arranged to have orthogonal polarizations. It is to be noted that when this is done the reflector must be able to reflect radiations of both polarizations so that if it consists of a set of parallel conductors a second set at right angles to the first is necessary. The two sets of parallel conductors may define different outlines of the same parabolic surface as indicated in Fig. 10. This shows a suitable arrangement for a conical scan position determining beam and a beaver tail search beam. Specification 746,629 also is referred to.