GB646357A - Short wave directive radio antennae - Google Patents

Abstract

646,357. Aerials;radio navigation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Mav 29, 1945, No. 13491. Convention date, May 26, 1943. [Class 40 (vii)] A short wave directive antenna is formed by attaching a conductive rectangular flap 12 along one edge to a conductive base sheet 10 so that there is a small angle between them. The base sheet may be large, e.g. the side of an aircraft fuselage. The triangular ends of the antenna are preferably closed and a curve (Fig. 15, not shown) relating width to length for an antenna with ends closed is given. To prevent ingress of dirt and moisture, the open bottom edge may be filled with dielectric material. Connection to the antenna can be made by means of a coaxial feeder 15, the outer sheath being connected to the sheet 10 and the inner conductor to a point mid-way along the flap. The vertical distance of the connection from the edge of the flap may be chosen to give a particular terminal impedance. Maximum radiation occurs downwards along a line making an angle of 45 degrees with the sheet 10 and at right angles to the line of attachment of the flap; to increase the directivity a second reflector flap 22 may be mounted above the radiator with its open edge just overlapping the latter's attached edge. The units may be tuned either by U-shaped adjustable attachments 13 and 23, or by using a capacity plate mounted on a threaded rod screwed through a boss on the lower edge of the reflector, Fig. 11 (not shown). The antennae may be mounted in arrays, an array of four antennµ with reflectors and fed in phase by branched feeders tuned by stubs is described with reference to Figs. 8 and 12 (not shown). Radio navigation.-In order to estimate drift an aircraft 1, Fig. 2, fitted with the antennµ described, radiates two lobes of energy Pb and Sb of the same frequency downwards at an angle of 45 degrees. After diffuse reflection by the land or sea surface S, energy is received by the same aerials and the signals from the port and starboard sides are compared in frequency, the beat frequency being proportional to the craft's rate of drift.