Patent GB-1472455-A (GB)
Title: Non-rotating antenna
IPC: G01S1/50
Filed: 1974-06-12
Abstract: 1472455 Aerials INTERNATIONAL STANDARD ELECTRIC CORP 12 June 1974 [15 June 1973] 26075/74 Heading H4A A method of producing a 135 Hz modulation component by step-wise rotation of a binary current distribution around a cylindrical radiating array of active elements, for superposition on a rotating limacon radiation pattern of the type radiated by Tacan antennnas comprises generating a first signal having a first current amplitude and first phase; generating a second signal having a second current amplitude and second phase; feeding a first predetermined group of a plurality of active elements on said array with said first signal, said group being located non-symmetrically around said cylindrical array; feeding the remainder of said active elements with said second signal; and electroni. cally switching said active elements whereby said group is electronically rotated around said cylindrical array. As described, a TACAN beacon aerial system 2, Fig. 2, comprises an inner conductive circular cylinder 5, around which are disposed 96 equally spaced aerial arrays 6, each comprising three collinear dipole radiators 1. The arrays and their feeders may be printed upon dielectric sheets. Further dipole radiators may be increased in the arrays to obtain a desired vertical pattern shaping. R.F. power is supplied to modulator and transformer sections 3, where an H 11  mode is generated in a coaxial waveguide and rotationally stepped at the 15 Hz rate by means of sequential signals from a control unit 8 to 32 ZIN switching diodes. The moded signal is tapped from the coaxial line by 96 equal spaced radial lines in a power divider section 4, and the arrays 6 are fed therefrom through a switching section 7 in which 96 PIN diodes are controlled by signals from the unit 8 to obtain the 135 Hz modulation by cutting off input to a selected 18 arrays at a time, and stepping at the appropriate rate around the aerial system. In practice however, the complete cutting off of current to the 18 elements would cause induced current changes in adjacent elements which in turn would produce an induced current in the nominally cut-off elements. To overcome these effects, the "cut-off" elements have an "antiphase" current fed to them to cancel out the last mentioned induced current.- The selected 18 arrays comprise three groups of 6 adjacent arrays each, the groups being symmetrically disposed around the aerial system with each group separatedfrom adjacent groups by 26 arrays to which signals are fed. Stepping is by two adjacent arrays advancing one array space at a time, in all groups simultaneously, at a 45 Hz rate. The control unit 8, Fig. 3, generates command signals for the PIN diode switches in the system. It comprises two recirculating shift registers 10, 11, each containing 96 flip-flops and clocked by respective clock generators 15, 14. The clock generator 15 has three times the frequency of the clock generator 14, both being controlled by a crystal oscillator 16. The shift register 11 controls the states of the 32 PIN diodes of the modulator/transformer 3, Fig. 2, through drivers 12. At any instant three of said diodes are conductive and stepping by one diode spacing is effected in three stages, the three clock pulses. Thus if diodes 1, 5, 9 are conductive, a first pulse changes this to 1, 5, 10, a second pulse to 1, 6, 10 and a third pulse to 2, 6, 10. Thus, 96 pulses are required to effect a complete rotation. The shift register 10 controls the states of the 96 diodes in the switching section 7 through drivers 13. At each clock pulse an adjacent pair of arrays in each of the said groups is effectually stepped forward by one array space. The three pairs being stepped at any instant are 120 degrees apart. It takes three pulses from the clock 15 to step all members of the groups forward one space, 96 pulses to step them into each others immediately previous positions, and 3 Î 96 pulses to step them into their starting positions. The original initial conditions appear in the shift register 10 every 1/45 second but to ensure no false information is propagated for more than three cycles the register is then cleared and preset by a generator 17, which also operates at every cycle on the shift register 11. The control unit 8 comprises 135 and 15 Hz clock generators 18, 19 which control the generator 17 and a means 20 generating an auxiliary reference trigger.