GB688374A - Improvements in or relating to dielectric antennae - Google Patents

Abstract

688,374. Aerials. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. Feb. 18, 1949 [Sept. 2, 1948], No. 4520/49. Class 40 (vii). A dielectric antenna for use at very high radio frequencies comprises a body of dielectric material having the form of a circular sector of a volume of revolution whose material thickness measured in a direction parallel to the axis of revolution is small compared with the overall dimensions in a plane perpendicular to the said axis, said body having means to connect it to a transmitter or receiver, the directivity being substantially constant in all planes containing the revolution axis of the antenna and lying within the angle of the sector. A block 1 of insulating material such as polythene or polystyrene has the shape of a sector of a body of revolution about axis XX, the upper and lower surfaces 2 and 3 being plane and perpendicular to axis XX. The thickness between surfaces 2 and 3 is small compared with the radial dimensions of the body which extends over an angle of some 270 degrees and is limited angularly by plane surfaces 9 and 10 which may be metal-coated to act as reflectors. A coaxial transmission cable 6 is led into a recess 5 on axis XX, and the inner conductor is formed into a loop 7 to energize the antenna. In the Figure the loop is shown withdrawn from the recess for clarity. Radiation is concentrated in a plane perpendicular to axis XX and extending for an angle corresponding to the sector (about 270 degrees). For maximum directivity the thickness E is made substantially equal to where # is the wavelength in vacuo and e is the dielectric constant of the material. In the modification of Fig. 2 (not shown), the surfaces 2 and 3 are shallow cones, having their apexes outwards to provide better matching to space but with some loss of directivity. In Fig. 3 (not shown), the surfaces 2 and 3 again comprise cones but with their apexes in the same direction, giving a directivity pattern in the form of a sector of a hollow cone having axis XX and a vertical angle lying between the vertical angles of the two conical surfaces 2 and 3. The embodiment of Fig. 4 (not shown), is similar to that of Fig. 1, but the surface 2 is coated with a metal reflector having a central aperture for the feeder cable and gives a conical sector directivity pattern having axis XX and sides directed slightly away from the reflecting surface 2. Fig. 6 (not shown) utilizes two antennµ as in Fig. 1 but each limited to 180 degrees, attached respectively to the leading and trailing edges of an aircraft wing to give omnidirectional directivity in a horizontal plane, while Figs. 7 and 8 (not shown) each comprise one such antenna below an aircraft wing to give downwards and fore-and-aft or transverse directivity, respectively, in a vertical plane. The antennµ may be used for transmission or reception, and may be combined with known non-directional aerials or reflectors of known construction to vary their directivity patterns.