Patent GB-744982-A (GB)
Title: Localizer antenna system
IPC: H01Q21/08
Filed: 1952-09-16
Abstract: 744,982. Radio navigation; aerials; aerial couplings. ALFORD, A. Sept. 16, 1952, No. 23215/52. Class 40 (7). An overlapping-beam beacon defining an equi-signal approach path C, Fig. 2, produces two simultaneous overlapping uni-directional beams A and B modulated at 90 and 150 c/s respectively and two simultaneous overlapping broader auxiliary holes D and E modulated with the same frequencies but whose carrier frequency differs from that of the beams by 5-20 Kc/s and whose radiation is directed more to the side and rear of the approach path so that an aircraft approaching, the landing area from any direction can detect the guidance signals but the main beams are not affected by reflecting objects in the field of the auxiliary lobes. The main beams A and B are produced by a collinear array of six horizontal dipoles 1 ... 6, Fig. 1, backed by reflectors 1<SP>1</SP> ... 61, dipoles 2 ... 5 being #/2 slot-fed elements and the end elements 1 and 6 being full-wave tubular dipoles each comprising two collinear #/2 elements as described below. The main carrier frequency from source 20 is applied via the 90 c/s and 150 c/s electro-mechanical modulators 33 and 34 to opposite inputs of a transmission line bridge 21 and the carrier and both sets of sidebands are applied from the upper output via balun 3b, line 14 and coaxial line bridge 7 cophasally to dipoles 3 and 4 to produce a # dumb-bell " pattern, Fig. 3. At the bottom output of bridge 21 the carrier is suppressed due to the crossover in arm 40 and the two sets of sidebands are in anti-phase and are applied to dipoles 1 ... 6 via balun 35 attenuator 37, transformer 8 and bridge 7 in such manner that the 90 c/s sidebands are applied cophasally to dipoles 1, 2 and 3 and in opposite phase to dipoles 4, 5 and 6, the 150 c/s sidebands being applied to dipoles 1 ... 6 in a similar manner but in opposite phase relationship to produce a " clover-leaf " pattern, Fig. 7, which combines with the # dumb-bell " pattern of Fig. 3 to produce the required beams A and B, Fig. 2. In Fig. 10 which shows the relative phases of the signals applied to the six elements of the array, X and Y denote signals from the lower and upper outputs respectively of bridge 21, F denotes the carrier frequency signal and S1 and S2 denote the sidebands resulting from modulation by the 90 and 150 c/s signals respectively. The attenuator 37 is adjusted so that the relative power of the Y and X signals is 4 : 1 approximately. The auxiliary lobes D and E, Fig. 2, are produced by applying the auxiliary carrier from source 19 via 90 c/s and 150 c/s electromechanical modulators 25, 26 to slotted cylinders 15 and 16 respectively. The main and auxiliary modulators 33, 34 and 25, 26 may be driven by a common motor or as shown by two synchronous motors 30 and 22. The full-wave dipoles 1 and 6 of the main array each comprise two tubular T members 51, 52, Fig. 9, with the #/2 cross-bars 55, 63 disposed collinearly. The aerial is fed through the leg of member 51, the outer cylinder 53 and inner cylinder 54 forming a coaxial transmission line and the top of the inner cylinder being connected by a strap 57 to an axial conductor 56 insulated from cross-bar 55 and connected to cross-bar 63 of T member 52 by a strap 59.