GB606927A - Improvements in antenna systems - Google Patents

Abstract

606,927. Directive radio systems. WESTERN ELECTRIC CO., Inc. Jan. 22, 1946, No. 2086. Convention date, Jan. 24, 1945. [Class 40 (vii)] A highly directive aerial system comprises a pair of cylindrical-parabolic reflectors facing each other and having mutually perpendicular focal lines, an aerial element being coincident with one of the focal lines. Figs. 1 and 3 and Fig. 2 (not shown) illustrate such a system in which an aerial 10 comprising an extension of the central conductor of the coaxial transmission line 2 is aligned with the focal line 5 of an auxiliary horizontal cheese reflector 3 comprising a short vertical parabolic cylinder with end plates 7 and 8 spaced apart a distance D less than #/2 and having a rectangular aperture 9 which radiates into the main reflector 13 comprising a horizontal parabolic cylinder, the focal line of which, 15, is coincident with and equal in length to the horizontal dimension of the rectangular aperture 9. The auxiliary and main reflectors may be regarded as controlling the horizontal and vertical directivity respectively and the angular aperture # of the main reflector is adjusted in relation to the vertical dimension D of the aperture 9 to produce a pencil beam with a plane wave front. In a modification, Fig. 4, the system is cut in two by a horizontal plane reflector 25 and only the upper half is utilized. In this case the vertical directivity is reduced and the upper half of the vertical polar diagram follows an approximate cosecant distribution which is the ideal shape for a radar system used for the detection of long-range aircraft. In a further modification of this type, Figs. 5 and 7 and Fig. 6 (not shown), the auxiliary reflector 3 is inclined at an angle to the horizontal and is mounted in a wooden framework 43 with horizontal reflecting platforms 46 and 47. The focus 38 of the auxiliary reflector is near its aperture and the aerial element mounted adjacent the focus comprises a polystyrene plug 50 fed by a wave-guide 49, the surface of the plug facing the main reflector 13 being shielded by a brass member 51. The whole structure is made of wood and the reflecting surfaces of the parabolic cylinders and of the platforms 46 and 47 are covered with copper foil. Suitable dimensions are given for an operating wavelength of 9.8 cms. and Figs. 8 and 9 (not shown) illustrate the horizontal and vertical polar diagrams produced by such a system.