GB1247270A - Scanning microwave waveguide aerial - Google Patents

Abstract

1,247,270. Aerials. MULLARD Ltd. 28 July, 1969, No. 37785/69. Heading H4A. A wideband aerial comprises an axially extending row of equally spaced radiating holes along a hollow waveguide, and an elongate dielectric member inside said waveguide. The length and breadth of each hole are substantially equal (e.g. they are circular or generally square) but their relative sizes may be systematically varied along the row, to reduce side lobes or otherwise modify the radiation diagram. The dielectric member effectively lowers the waveguide wavelength below the corresponding free space wavelength so that grating lobes may be controlled and eliminated, mathematical formula which must be satisfied being given. The dielectric member is made of a low-loss material, such as polystyrene, and may wholly or partially fill the waveguide under the array of holes, and be tapered for matching at the fed end. As described, the waveguide has a rectangular cross-section. A single row of holes may be provided along the centre line of a narrow wall (Fig. 4, not shown) or along a line parallel to the centre line of a broad wall (Fig. 5, not shown) or two rows of symmetrically staggered holes may be provided on lines parallel to, and at equal distances on each side of the centre line of a broad wall (Fig. 6, not shown). In all cases, the spacing between adjacent holes of a row is Xgo, where ygo = wavelength in the waveguide when the beam is perpendicular thereto. Dielectric material, generally having a dielectric constant higher than that of the material in the waveguide may be provided for the holes to increase the power radiated therefrom. This may take the form of a continuous slab outside the waveguide covering the holes (Figs. 8a, 8b, not shown) or of such a slab including stud-shaped pieces entering the holes (Fig. 7, not shown), or separate disc or stud-shaped pieces may be provided for each hole (Fig. 8c, not shown). Scanning by frequency modulation may be provided, and Specification 1,105,758 is mentioned.