GB637729A - Antenna - Google Patents

Abstract

637,729. Aerials. STANDARD TELEPHONES & CABLES, Ltd. Jan. 10, 1947, No. 974. Convention date, Jan. 12, 1946. [Class 40 (vii)] In an aerial radiating horizontally polarized waves in a uniform horizontal pattern comprising a hollow conductive cylinder 10 mounted vertically and having a slot 11, 12 with a short circuit 28 at one end and open at the other, and with a feeder 27 energizing the cylinder at the open end of the slot to produce equal and opposite potentials along the edges of the slot, the cross-sectional area of the cylinder is so chosen that the voltage distribution along the slot is in the form of a standing wave, one-quarter wavelength of which is not less than 0.4 of a free-space wavelength. To achieve this, the cross-sectional area is chosen to be between .0113#<2> and .0177#<2> with a preferred value less than .0154#<2>. In order that all com - ponents of the circumferential flow of current should be substantially in phase, thereby producing maximum radiation in the plane perpendicular to the cylinder axis, the cylinder is cut to a length less than 0.45 of a free-space wavelength with a preferred length between 0.2 and 0.4 wavelength. The slot has a width about one sixth of the diameter and is closed by a strip 31 of insulating material. The upper end of the cylinder is closed by an insulating dome 33 and the lower end by a plate 28 which provides the shortcircuit across the slot. An adjustable shorting bar may be provided. For support, the cylinder may be attached to a metal pole 30 along the line of zero potential opposite to and parallel with the centre line of slot 11, 12. The transmission line enters the cylinder through the plate 28, the line outer being in contact with the plate. Since this is a point of zero potential the outer is not energized and does not disturb the radiation pattern. Crosssections of any shape may be employed and aerials having circular, elliptical, rectangular and triangular cross-sections are described, Figs. 5, 6 and Table II (not shown). Specification 515,684 is referred to.