GB769165A - Improvements in circularly polarised microwave antennae - Google Patents

Abstract

769,165. Aerials. STRAUCH, R., ALLEZARD, R., and MENU, J. May 13, 1955 [May 15, 1954], No. 13850/55. Class 40(7) An aerial for the radiation of circularly polarized waves comprises a flat circular disc excited, at a plurality of points distributed round a circle on one of the faces of the disc, by wave energies having respective phase differences equal -to the angular distances apart of the points to which they are applied. The aerial gives a substantially circularly polarized field over a wide beam angle. As shown, the circular disc 12 is mounted inside a dielectric housing 2 at the end of a metallic support cylinder 1. The coaxial feed 3 is led into the cylinder 1 at the opposite end to the disc 12 and is coupled to a cavity 5. Leading from the cavity are N equi-angularly distributed coaxial lines the extensions of whose inner conductors (7, 9) couple them tc the cavity. The diameters of the cavity and coupling probes are arranged to be such that energy from the input is entirely transmitted to the N coaxial lines. These lines extend through the centre part of the cylinder 1 and their inner conductors (7<SP>1</SP>, 9<SP>1</SP>, 10<SP>1</SP>) extend beyond into the dielectric housing 2 and are connected to the disc 12 at N points spaced round a circle. The N lines in the centre part of the cylinder are filled with varying lengths of dielectric to establish the required phase differences. The dielectric material is preferably arranged in pieces 14 all but one of which in any line is of a length which is a multiple of a quarter wavelength. The extensions 7<SP>1</SP>, 9<SP>1</SP>, 10<SP>1</SP> of the central conductors of the N coaxial lines each serve as an impedancematching transformer and their length and diameter are determined experimentally to effect impedance match. Twice the diameter of the disc 12 less the diameter of the circle around which the points of excitation are arranged should be approximately half of the working wavelength. A metallic ring 15 screwed to the cylinder 1 is provided to eliminate back radiation. Specifications 567,201 [Group XL] and 650,622 are referred to.