GB629893A - Improvements in or relating to radio aerials - Google Patents

Abstract

629,893. High-frequency electric transmission lines. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 3, 1946, No. 19956. Convention date, July 4, 1945. [Class 40 (viii)] [Also in Group XL (c)] An arrangement for coupling a transmission line to a slot-type aerial comprises a triangular plate within a resonant chamber mounted behind the slot having its base connected to the edge of the slot and a transmission line connected to the apex of the triangular plate. As shown in Figs. 1 and 2 a pair of 90 degree slots 12 and 14 and a central slot 16 forming a pair of radiating triangular members 18 and 20 are provided in a plane conductive surface 10 (e.g. airplane fuselage) behind which is fastened a metal pan 22 forming cavities 21, 23 having an effective depth of #/4 and serving to isolate the triangular members from the sheet 10. The members are energized by means of a triangular feed-plate 26 having its base connected to one edge of slot 16 and its apex connected to a transmission line TL and contained within a resonant feed chamber 24. An aerial of this type is stated to have low magnitude side lobes and to be relatively small and the standing wave ratio is stated to be less than 2 : 1 over a frequency variation of 16 per cent of the mid-band frequency. It may be reduced in size by capacity loading at the free ends of the radiating members or by omitting the boundary slots, the former reducing the band width and the latter increasing the side lobes in the radiation pattern. A modified construction in which the boundary slots are omitted is shown in Figs. 4 and 5 and comprises two slots 38 and 40 lying diagonally across rectangular cavities 34 and 36 having a side length of 0.55# and a total depth of 0.07#. A prismatic conductive strip 42 of triangular cross-section is connected to the sheet 10 between the slots and to cavity 34 by means of studs 44, 46 which ensure that only the desired mode of oscillation can be set up in the cavities. This standing wave ratio with this construction is low and substantially constant for bandwidths of about 18 per cent of the mid-band frequency but rises abruptly at the low frequency end of this range and thus provides a high-pass filter characteristic. A further modification, Figs. 7 and 8 (not shown), comprises an arrangement similar to the construction of Figs. 4 and 5, but with the rectangular cavities folded back to back against one another. In this arrangement the input impedance may be varied by varying the spacing between the apex of the feed triangle and a side wall of the cavity. All the constructions described may be protected against weather conditions by filling the slots with an insulating material such as polystyrene or lucite. Specification 592,180 is referred to.