GB575534A - Improvements in or relating to antennas for ultra high frequency electromagnetic waves - Google Patents

Abstract

575,534. Wave guides. WESTERN ELECTRIC CO., Inc. March 22, 1944, No. 5389. Convention date, Dec. 17, 1942. [Class 40 (v)] An antenna for ultra-high-frequency waves comprises an antenna element consisting of an unsheathed dielectric rod, a portion of the length of which has a tapering cross-sectional area and another portion of uniform crosssectional area. Fig. 1 shows an antenna having a good end-on characteristic and comprising a rod 1 of low-loss dielectric such as polystyrene mounted in a holder 3 which serves as a wave guide for connection to a translating device, not shown. The rod is six wavelengths long and has an electric plane transverse dimension a which is uniform throughout the length of the rod. The magnetic plane transverse dimension b tapers uniformly from the fixed end 4 of the rod to a point 5 and is then uniform from point 5 to the free end 2 of the rod, which is rounded. In the example shown, the tapered part 7 is somewhat longer than the uniform part 8. With this configuration, the phase velocity of H11 waves in the rod varies from point' to point in such a way as to give an improved end-on characteristic. A similar rod having a circular cross-section, and with tapered and uniform parts of unequal length is also described (Fig. 2, not shown). Fig. 3 shows a dielectric rod of circular cross-section in which the tapered part 7 is equal in length to the uniform part 8. The rod is 7.23 wavelengths long. This configuration gives the best characteristic. The characteristics of the three embodiments as compared with known antenna of the dielectric rod type are described (Figs. 5-8, not shown). Fig. 9 shows a mounting 42 for coupling a circular polystyrene antenna rod 10 to a coaxial line 45, 46. Inner conductor 46 is connected to an exciter wire 49 fixed diametrically in the butt of rod 10 and extending into a tuning stub 48 having an adjustable piston 55. Wire 49 is connected at 52 to the mounting 42. The length of wire 49 between 52 and 55 serves to terminate line 45, 46 in its characteristic impedance. Waves supplied by the coaxial line to the exciter wire 49 establish in rod 10 transverse electric waves linearly polarized in the plane of wire 10. The antenna will also serve to receive wave components similarly polarized. For use with circularly polarized waves in rod 10, the necessary conversion is effected by a pair of critically spaced polar reactances in the form of wires 56 arranged at 45 degrees to wire 49. U.S.A. Specification 2,236,393 is referred to.