GB1375680A - - Google Patents

Abstract

1375680 Aerials INTERNATIONAL STANDARD ELECTRIC CORP 16 Aug 1973 [16 Aug 1972] 38719/73 Heading H4A A directive beam aerial arrangement comprises a central driven monopole element P, Fig. 2, and S sets of parasitic elements, each comprising one reflector and p directors, arranged in respective radial planes at angular spacings of # = 360 degrees/S. The elements are disposed normally to a circular metal ground plate, and they have heights of approximately a quarterwavelength at the operating frequency. A feed source is connected between the base of the driven element and the ground plate, and a diode 2, Fig. 3, is connected between the base of each parasitic element and the ground plate. By applying suitable bias voltages through a choke 3 the diode 2 may either be rendered substantially non-conductive, when the associated parasitic element is ineffective, or said diode may be rendered conductive, when the associated parasitic element becomes effective. As shown, three directors are provided in each radial plane, as well as a reflector. The beam from the aerial arrangement may be directed along any of said planes, by rendering the diodes associated with the parasitic elements therein conductive. Additional directivity may be obtained by making other directors effective, as shown in Fig. 4. Here, as well as the reflector R 1 and the directors D 1 , D 2 , D 3 along the beam axis, directors A, A<SP>1</SP>, B, B<SP>1</SP>, C, C<SP>1</SP>, are made effective. The reflector and the additional directors all lie approximately along a parabola which has P as focus. A control arrangement for providing step-by-step rotation of the beam is described with reference to Fig 7 (not shown). This comprises an S-stage shift register, which is stepped by clock pulses and is re-set by means of a flipflop connected to its first and last stages. Output from each stage of the shift register is utilized for biasing the diodes of the associated parasitic reflector and director elements. Since each director is used three times during each beam rotation, i.e., once when it is in line with the beam axis, and twice when it forms part of a parabolic reflector (Fig. 4), outputs from three stages of the shift register are coupled through an OR-gate to each director diode.