GB798821A - Improvements in or relating to aerials for metric, decimetric or centimetric waves, of flat form and capable of being applied to flat surfaces - Google Patents

Abstract

798,821. Aerials. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. March 15, 1956 [March 17, 1955], No. 8208/56. Class 40 (7). An aerial arrangement of flat form, and therefore particularly useful for mounting on aircraft, comprises a transmission line for the energy to be radiated the structure of which is such that its cross-section is not completely surrounded by conductive material and there are sudden variations along its length causing sudden impedance variations which act as radiation sources. In one form the line may consist of a dielectric plate 1 provided with a metallic coating 2 on all its sides except for a channel on the top surface which extends round fingers 3, 31, 4, 41, 5, 5<SP>1</SP>, attached alternately to opposite edges. To produce radiating impedance variations as required by the invention a variety of arrangements may be used. For example the width of the channel at the end of certain fingers may be reduced as at 7 and 7<SP>1</SP>. In another arrangement the width of the channels between the fingers and the finger widths are reduced over short lengths of the line (Fig. 4, not shown). In a further arrangement the lengths of the fingers are reduced and the edge coatings to which they are attached are brought closer together (Fig. 5, not shown). If the line is located inside a metal casing which is open at the front, spaced shielding plates extending at intervals across the front of the line and attached to the sides of the casing may be used to produce the discontinuities (Fig. 6, not shown). The dielectric in the line may be a solid or it may be air, in the latter case the conductive parts require to be more robust as shown in the construction of Fig. 3. This Figure also shows how the transmission line may be fed from a coaxial feeder 24 by insulating one of the fingers 13 of the line from the other conductive parts of the line and connecting the inner conductor 25 of the feeder to this finger. Fig. 11 shows a different type of transmission line in which a ceramic plate 31 has a metal plate 40 on its underside and a narrow metallic band 32 on its upper side. Radiation may be obtained by reducing the width of the strip as shown at e<SP>2</SP>, or by introducing sharp turns in the band. In another arrangement the band is supported above the base plate by spaced supports having a high dielectric constant which themselves form the radiating discontinuities.