GB624091A - Antenna - Google Patents

Abstract

624,091. Aerials; coupling arrangements. RADIO CORPORATION OF AMERICA. July 8, 1946, No. 20345. Convention date, Aug. 25, 1945. [Classes 40 (v) and 40 (vii)] [Also in Group XL (b)] An ultra-short-wave aerial comprises a resonant cavity formed by a quadrangular conductive base, one wall of which is provided with an elongated slot of a width -small compared with the width of the wall transverse to which and within the box is positioned a conductor for energy transfer between the aerial and associated apparatus. In one arrangement, suitable for mounting flush with the exterior surface of e.g. an aeroplane, an elongated slot 20, Figs. 1 and 2, is formed in the front wall 12 of a conductive box 10 and energy transfer between the aerial and transmitting or receiving apparatus is effected by means of a transmission line TL connected through a socket 52 to one end of a conductor 60 mounted transversely to the slot 20, the other end of conductor 60 being connected through a second socket 52 to a short-circuited stub 73. Variation of the coupling between the cavity and conductor 60 is effected by varying the distance between 60 and the rear wall of the cavity and for this purpose conductor 60 is eccentrically mounted at 62, 63 so that the necessary variation is brought about by rotation of 60. The ends of the slot are isolated by means of transverse slots 22, 24 and the cavity is tuned by adjustment of capacity plates 26, 28, 30. A window 44 of dielectric material, e.g. polystyrene, carried by a bezal member 45, prevents the entry of dust, moisture, &c. Band-pass curves, Fig. 3 (not shown), indicate that the standing wave ratio is less than 1.8 over a frequency range extending from 422 mc/s. to 478 mc/s. In an alternative arrangement, Fig. 4 (not shown), the conductor 60, the sockets 52 and the stub 73 are replaced by a coaxial extension of one of the sockets 52 across the box 10 and the inner conductor of the extension is provided with a capacity plate adapted to co-operate with a similar plate connected to the side wall of the box. In a further arrangement, Figs. 5 and 6, the transmission line is coupled to the cavity by means of a curved and tapered tongue 90, to the apex of which the transmission line is connected and the broad base edge of which is connected with the side wall 16 along its entire length. By suitably selecting the taper and curvature of the tongue 90, a constant input impedance results over a relatively wide frequency band. In another arrangement, Fig. 7 (not shown), the tongue is U-shaped in cross-section and the base portion is connected with the rear wall of the box.