Patent GB-1012029-A (GB)
Title: Antenna structure and system
IPC: G01S1/02
Filed: 1962-07-10
Abstract: 1,012,029. Aerials: radio-navigation. A. ALFORD. July 10, 1962, No. 26532/62. Headings H4A and H4D. In an aerial system suitable for a TACAN ground station a number of vertical dipoles 32, Fig. 1, mounted at equal intervals around, and spaced a quarter-wavelength from a metallic tubular reflector 30 are connected by coaxial cables 31 to outlet sockets 38 of a scanner 22, comprising a stator and a rotor between the opposing surfaces of which is a wave-guide space connecting sockets 38 to a single central coaxial socket 52, the transmission characteristics between each socket 38 and the socket 52 varying repetitively as the rotor revolves because of angularly disposed attenuating and delaying features incorporated upon its surface. As described, scanner 22 comprises a housing 36, Fig. 7, to which is fixed a medial annular conductor 44 with a number of radial conductors 42 extending therefrom and leading to the centre conductors of the socket 38. The rotating portion of the scanner revolves on bearings 90, 92 mounted in a journal box fixed to the housing and it comprises a mounting disc 108 which carries an inner annular conductor 43, an outer annular conductor 112 and a number of dielectric elements 48. The socket 52 is mounted on the stator so that its outer conductor is connected to medial annular conductor 44, with its centre conductor supported by an insulator 120 and extended with small clearance into a bore 96 in the rotor by one quarter-wavelength, so that it is virtually connected to the rotor inner annular conductor 43 at its upper surface. A similar method utilizing a rim 126 provides a virtual connection across the gap 134 between the outer periphery of the rotor and the inside of the housing contiguous with the outer conductors of the sockets 38. A waveguide region 46 is formed between the stator and the rotor, the upper boundary of which, i.e., formed by the lower surface of the medial annular conductor 44 and the lower surfaces of the radial conductors 42, is flat. The lower boundary of the waveguide region comprises the upper surface of the inner annular conductor 43 which is so shaped that the gap between it and conductor 44, considering a fixed plane containing the axis of the scanner, varies as the rotor is turned as a function of (a 1 +b 1  cos#), where # is the angle of rotation and a 1  and b 1  are constants (Fig. 5, not shown). The dielectric elements 48, Fig. 4, comprise piano-cylindrical lenses of uniform thickness which are carried by the outer annular conductor 112, into which they are recessed in order to maintain the value of the characteristic impedance of the waveguide region the same in spite of the increased net dielectric constant they cause. As applied to TACAN, nine dielectric elements 48 are symmetrically placed around the rotor and as it rotates the energy fed to each aerial is varied during a revolution through one cycle because of the shaping of inner annular conductor 43 and superimposed on this variation are nine cycles of variation owing to the effect of the dielectric members 48. For operation at 1000 mc/s. the rotor diameter is 13 inches and the gap between inner annular conductor 43 and medial annular conductor 44 varies from 0À11 inches to 0À21 inches. For a dielectric constant of 15, members 48 are 0À2 inch thick and are recessed 0À1 inch below the surface of the outer annular conductor 112. In another embodiment (Fig. 8, not shown) the function of the di-electric members 48 is performed by a shaping of the outer part of the surface of the rotor similarly to that of the inner annular conductor as described above, but with nine instead of one elevations or depressions, i.e., so that the gap between it and the underside of the stator is a function of (a 2  + b 2  cos 9#), where # is the angle of rotation and a 2  and b 2  are constants (Fig. 9, not shown). As applied in particular to TACAN, the scanner may be provided with means for triggering reference signals for the main limacon of the radiation pattern (Fig. 2, not shown) and for each of the nine subsidiary lobes thereof, comprising a single magnetic slug 68, Fig. 1, positioned at one point on the periphery of the rotor, and nine equally spaced magnetic slugs 66, positioned around the rotor in another plane, and associated pulse generating coils 72, 70. The pulses are fed to reference generators 76 (L.F.) and 74 (H.F.) which are connected to an encoder 62, together with an identification call generator 78. A receiver 58 and a transmitter 60 are connected through a duplexer 56 to input socket 52 of the scanner. The receiver is connected via a distance reply generator 64 to the encoder 62.