Patent GB-592180-A (GB)
Title: Improvements in or relating to short-wave antennae
IPC: H01Q13/10
Filed: 1944-09-15
Abstract: 592,180. Aerials; electric resonators. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 15, 1944, No. 17735. Convention date, June 27, 1942. [Classes 40 (iii) and 40 (v)] A short-wave antenna is embodied in the wing or the side-wall of an aeroplane and comprises a conducting sheet backed by a resonant cavity and flush with the surface of the wing or wall. In the embodiment shown in Figs. 1 and la, cavities 23 are formed at the edge 21 of a wing. Each cavity has a parabolic back surface 23 which is a quarter of a wavelength behind a half-wave dipole 25, and may have a plastic window conforming to the shape of the wing. Instead of the dipoles 25 and windows, metal windows in the form of curved strips somewhat less than a wavelength wide may be provided and may act as radiators, Fig. 3 (not shown). At their edges are slots which may be closed with insulating material to avoid aerodynamic disturbance, and the cavities enclosed by them may be resonant. The directivity may be sharpened and side lobes be eliminated by locating parasitic halfwave dipoles about one-eighth of a wavelength in front of the primary radiators, Fig. 5 (not shown). In a further modification, a strip of the side wall of the plane, almost half a wavelength wide, is bounded by vertical slots about a wavelength long and backed by a cavity about one-eighth of a wavelength deep, Fig. 7 (not shown). The metal strip, which constitutes an antenna, is connected at the inner edge of one slot to the inner conductor of a coaxial feeder, and the wall of the cavity to the outer conductor. Alternatively, a symmetrical radiation pattern may be obtained by connecting a two-wire transmission line to the opposite edges of the strip, Figs. 9, 9a. (not shown). A stack of antennµ of this kind may be formed, and in a further modification, Figs. 11, 13, the slots 52 between the radiating strips 30 may have in-turned ends 56, to permit of the stacking of several parallel arrays of the kind shown in Fig. 11 without undue interference between adjacent arrays. The impedance of the antennµ depends on the length of the inturned ends 56, which may be adjusted to match the antennµ to the feeders. Side lobes are eliminated when the spacing between the slots is slightly less than half a wavelength, Fig. 12 (not shown). The antennµ 30 are energized by connecting the inner conductors of two coaxial lines TL1, TL2, Fig. 13, to their inner edges, while the outer conductors are connected to the back plate of the resonant cavities. The cavities have central partitions 60 and walls 62. In a further modification, Fig. 14 (not shown), the outer edges of the slots 52, 53 and 54, 55 may respectively be connected by the inner conductors, half a wavelength long, of two sections of coaxial line whose outer conductors are in contact with the antennµ 30 and are fed at their inner ends from a feeder connected through a phasereversing network of the kind described in Specification 487,708. The outer wall 30, 33 may be built flush with the wall 45 of the body of the plane or, when added to an existing plane, it may project and be streamlined as shown. For broadcasting, antennµ of the above type may be stacked in the form of a cylinder 73, Fig. 16. mounted on a tower 75, the slots being spaced half a wavelength apart and backed by cavities a quarter of a wavelength deep to which the high-frequency energy is fed, Fig. 17 (not shown). A set of similar slots at the nose of an airplane, Figs. 18, 19 (not shown), may be connected alternately to each of two eccentrically-connected transmission lines, so as to give a switched radiation pattern for direction-finding, and the directivity may lie sharpened by mounting parasitic half-wave dipoles in front of the slots.