GB640706A - Ultra-high frequency antenna - Google Patents

Abstract

640,706. Aerials. STANDARD TELEPHONES & CABLES, Ltd. Dec. 19, 1946, No. 37407. Convention date, Jan. 17. [Class 40 (vii)] A radio antenna comprises a hollow cylinder 3 having in its wall a single longitudinal slot 1, 2 with a short circuit at each end, and a feeder 6 coupled to the slot at a point 8 intermediate the short circuits, the crosssectional area of the cylinder being so chosen that the virtual wavelength of the voltage standing wave 11 produced along the slot is approximately twice the corresponding free-space wavelength. The cross-sectional area is less than .0228#<SP>2</SP> with a preferred value between .0154#<SP>2</SP> and .0115#<SP>2</SP>, the distance between short circuits being between A and 3# and the slot width, while not critical, of the order of .023#. When mounted vertically the antenna radiates horizontally polarized waves in a substantially uniform horizontal pattern, the vertical pattern depending on the location of the feed point 8 in relation to the short circuits. In a first condition, that shown in Fig. 1, the feed point is located centrally less than one half the virtual wavelength from each short circuit and results in a circumferential flow of current in phase at all points along the cylinder. The radiation produced has a maximum in the plane perpendicular to the cylinder axis. In a second condition, Fig. 2 (not shown), the feed point is displaced to be distant more than one half the virtual wavelength from one short circuit and less than one half the virtual wavelength from the other. The radiation in this case is in the shape of a bowl with the maximum at an acute angle to the cylinder axis. A third condition is considered, Fig. 3 (not shown), in which the feed point is located between one and one half the virtual wavelength from each short circuit resulting in a maximum of radiation in the plane at right angles to the cylinder together with other lobes which may be major or minor depending on the length of the cylinder. The slot short circuits may be provided by movable bars such as shown at 30 and 31, or plates 4 and 5, closing the cylinder ends. The slot may be closed by an insulating material. Specifications 515,684 and 592,180 are referred to. Reference has been directed by the Comptroller to Specification 635,343.