GB606124A - Directive antenna array - Google Patents

Abstract

606,124. Aerials directive radio systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 3, 1945, No. 20073. Convention date, Sept. 7, 1942. [Class 40 (vii)] A directional aerial array comprises a linear array of at least four dipoles arranged collinearly, and which are fed from or feed to translating apparatus with currents which vary along the array according to the coefficients of a binomial expansion, the dipoles being spaced apart at uniform intervals equivalent to between 270 and 480 electrical degrees. A directional characteristic may be obtained with such an array having a sharpness only obtainable with known types of "binomial" arrays with a spacing equivalent to 180 degrees by the use of a greater number of aerial elements and a consequent increase in the size of the array and complexity of the feeding apparatus. Fig. 1 illustrates a simple aerial array in accordance with the invention, in which dipoles 1, 2 3, 4 are supplied from the transmitter 5, the dipoles 1 and 2 being so fed via a shorted quarter wave transmission line transformer 8, that the current supplied to them is one-third of that supplied to the central units. A reflector is arranged 60 electrical degrees behind the array. In Fig. 3 is illustrated a radar system 30 comprising a pulse transmitter, a receiver, a cathode-ray tube display device and a blocking unit to allow common T.R. working. The aerial system comprises an array 43 of stacked dipoles, which consists of four rows of dipoles as shown in Fig. 1, arranged in a vertical array with a vertical spacing of a halfwavelength. The central antenna units are connected to the radar transmitter and receiver by the transmission line 44 and the rotary coupling unit 45. The outer antenna units are connected by lines 40 and 41 to a closed loop 52, which is then connected to the line 44 through a phasing unit 54 and power dividing network 55, the latter of which adjusts the amplitudes of the currents in the outer units to one-third of that of the central units. Coupled to the loop 52 is a pair of transmission line sections 60, 61 which are alternately tuned to resonance by the motor-driven condenser 62. When tuned to resonance, they operate as cut-off filters, as described in Specification 517,935, so that the energy supplied to the outer aerials is fed to the lines 40, 41 from the points 50, 51 alternately. The length of line between the points 50, 51 is a quarter-wavelength so that by adjusting the unit 54, the current in one set of dipoles leads and in the other set lags that flowing in the central dipoles by 45 degrees, whereby the polar diagram is alternately displaced to each side of the normal to the array, so that beam-switching is obtained. The switching device comprising the transmission line sections 60, 61 and the condenser 62 may be replaced by a mechanical switch actuated by a relay which switches the power alternately between the points 50 and 51, Fig. 5 (not shown). A modification, Fig. 6 (not shown), comprises an array as shown in Fig. 3 with the central stacks extended in a direction perpendicular to the dipoles by a further pair of dipoles added to each end of both stacks. These dipoles are fed with currents one-third of those supplied to the central elements, so that a further binomial array is obtained. The phasing of the currents supplied to the additional dipoles is also switched so that the beam successively occupies each of four equallyspaced directions lying on the surface of a cone. As shown, the array is arranged to operate with vertically polarized radiation, the whole array being mounted in the vertical plane, but turned through a right angle about a horizontal axis with respect to Fig. 3. It is stated in the Specification that the invention is also applicable to direction finders and to radio beacons. U.S.A. Specification 1,715,433 is referred to.