GB1387001A - Leaky coaxial cables - Google Patents

Abstract

1387001 Aerials SUMITOMO ELECTRIC INDUSTRIES Ltd 5 May 1972 [6 May 1971 21 Feb 1972] 21124/72 Heading H4A A leaky co-axial cable, which may be installed beside a vehicle track, is provided with an array of radiating slots or groups or slots along its outer conductor and has an electromagnetic wave delaying structure associated with its inner conductor. The period of axial spacing of the slots or slot groups p and the shortening ratio v (ratio of waveguide wavelength #g to free space wavelength #) are such that, so as to provide stable leakage wave radiation, i.e., so that, where γ n is the propagation phase constant in the radial direction of the cable, and n is an integer. The arrangement enables lower frequencies than usual to be employed, for example, of the order of 30 MHz. As described, an inner conductor wire 7, Fig. 3, is spirally wound on an insulating tube 6 and is supported within an outer conductor 9 by insulating means 8. Axially extending slots 10 1 , 10 2 , 10 3 , ... are provided in the outer coductor 9, which has a protective insulating sheath 4. In a second embodiment the inner conductor is of strip form instead of being a wire (Fig. 4, not shown). In a third embodiment, the inner conductor is constituted by a plurality of insulated wires which are wound side-by-side upon an insulating core, and the slots in the outer conductor are inclined to the axis of the cable (Figs. 5, 6, 8, not shown). In a fourth embodiment the slots in the outer conductor of the cable are arranged in groups with a minor constant spacing between the slots of each group and a major constant spacing between groups (Fig. 9, not shown).