Patent GB-587009-A (GB)
Title: Improvements in antennas
IPC: H01Q3/18
Filed: 1944-08-11
Abstract: 587,009. Directive aerials. WESTERN ELECTRIC CO., Inc. Aug. 11, 1944, No. 15397. Convention date, Aug. 14, 1943. [Classes 40 (iii) and 40 (v)] An antenna arrangement comprises an antenna element positioned in the focal plane of a paraboloidal reflector and rotatable about the reflector focus. The midpoint of the antenna element is preferably spaced from the focus. The half-dipole element 12 fitted with a corona 13 is secured to a conical member 14 secured to a conductor 6 forming the inner conductor of a coaxial line and rotated by a motor 7. The element 12 is threaded into the member 14 so that the distance of its mid-point 17 from the axis 3 can be adjusted. - A sector shaped reflector member 18 rotatable with the element 12 is secured to the shaft 6 through a quarter-wave sleeve 20 and a disc 21. A reflector ring 61 is mounted on the casing 60 between the element 12 and the reflector 1. The coaxial line 10 is connected to an energy transmitter or receiver 22 through a coaxial line 23, the outer conductor 25 being connected to the outer conductor 11 and the inner conductors being coupled through a quarter-wave sleeve 27. Opposite the line 23 is a stub tuning coaxial line 28 having its. outer conductor 30 connected to the conductor 11 and its inner conductor 29 connected to the sleeve 27. A plunger 31 adjusted axially by a knob 35 comprises inner and outer quarterwave cylindrical sleeves 32, 33 joined by an annular plate 34 forming an open-ended line with an adjustable impedance. The antenna 12 is coupled to the line 10 through serially connected quarter-wave impedance transformers 37, 38. The transmission line also includes an adjustable quarter-wave sleeve 42 and a fixed quarter-wave sleeve 43 connected to the conductor 6 through annular end pieces 45, form. ing quarter - wave transformers 48, 49, and separated by approximately a quarter of a wave length. A further impedance-matching transformer is constituted by the sleeve 27 and the inner surface of conductor 11. An impedance 51 comprising a quarter-wave sleeve 52 and disc 53 insulates shaft 6 associated with reflector 18 from the antenna element 12 and a further high impedance element comprising quarterwave sleeve 55, annular member 56 and inner surface of quarter-wave conductor 41 is utilized to prevent the antenna 12 from establishing standing waves in the outer surface of conductor 11. A short-circuited quarter-wave line 57 comprising quarter-wave sleeve 58 and annular member 59 presents a high impedance to energy conveyed from line 23 to line 10. The reflector 18-is spaced from the element 12 so that the waves reflected directly from the reflector 1 and after reflection from member 18 are in approximate phase agreement. The reflector 61 is adjusted to that the waves reflected or re-radiated are utilized to cancel or diminish the minor lobe of the directionalcharacteristic or field pattern produced by antenna 12 and reflector 1. The reflector 18 may be replaced by a dipole, or, in a modification, Fig. 8 (not shown), by a spherical reflector which may be fixed or rotatable, and the conical element 14 of Fig. 1 is replaced by an extension of the conductor, 6. Specification 450,484 is referred to.