Patent GB-1074735-A (GB)
Title: Improvements in or relating to directional beacons
IPC: G01S1/02
Filed: 1964-09-02
Abstract: 1,074,735. Aerials; .radio navigation. MARCONI CO. Ltd. Sept. 2, 1964 [Sept. 2, 1963], No. 35921/64. Headings H4A and H4D. In a speaking beacon of the kind in which a number of like fixed aerials 11-46 are spaced at regular intervals around a circle and are energized through a rotating or other commutating device 60, 62 so that those aerials contained at any time within one sector relative to that device are radiating directional information whilst the remainder are radiating a masking signal, a central omni-directional aerial 47 is provided, the arrangement then being that that aerial radiates carrier-frequency energy whilst the outer aerials radiate side-band energies only. As described, the 36 fixed aerials 11-46 are spaced at 10 degrees intervals around a circle of radius about 2À9 X, so that they are #/2 apart. Each aerial may be conventional three-element driven or parasitic array, or may be di-pole in front of a common circular or polygonal reflector, centred on the aerial 47 and made of wire mesh or rods, or may be an inclined long-wire travelling wave element in which case a central pole may support all the elements and the aerial 47. The commutating device connects five aerials at a time, for example Nos. 44, 45, 46, 11, 12 to an R.F. directional information feeder 59 whilst it connects the other thirty-one aerials, for example Nos. 13-43, to an R.F. masking signal feeder 61. A carrier frequency generator 51 supplies the aerial 47 directly and portions of its output are also taken to balanced modulators 53, 54, of known type. Audio frequency bearing information signals from a generator 55 modulate the carrier frequency in balanced modulator 53 and its output, containing only sideband energy, is taken by feeder 59 to segment 60 of the commutating device. If single sideband working is required, a filter 56 is interposed, which is high-pass or low-pass depending whether the upper or the lower side-band is used. Masking signals consisting of audio tone and/or noise from a generator 57 modulate the carrier frequency in balanced modulator 54 and its output is taken by feeder 61 to segment 62 of the commutating device, a filter 58 being interposed for single sideband working. The five aerials fed with directional information provide a narrow lobe radiation pattern, Fig. 2a (not shown), whilst the thirty-one aerials fed with masking signal provide a complementary radiation pattern with a minimum in alignment with the narrow lobe of the directional information signal, Fig. 2b (not shown). In operation, after sufficient dwell on a particular bearing for the relevant directional information to be given, the commutating device is moved by one step, for example, instead of aerials 44, 45, 46, 11, 12 being connected to feeder 59 and aerials 13-43 being connected to feeder 61, aerials 45, 46, 11, 12, 13 are connected to feeder 59 and aerials 14-44 are connected to feeder 61. The relevant directional information for the new bearing is then given, and stepping is continued. It is stated that the reduction in power handled by the commutating device because sideband energy only is applied to it allows the use of solid state switching circuits. In addition to the carrier frequency signal supplied to the central omnidirectional aerial, there may also be fed to it small proportions of the masking and/or directional information sidebands, suitably controlled in phases and amplitudes, whereby the null in the masking signal radiation pattern may be improved, Fig. 2c (not shown).