GB1247475A - Wide band antennas - Google Patents

Abstract

1,247,475. Aerials. THOMSON-CSF. 2 Feb., 1970 [4 Feb., 1969], No. 4941/70. Heading H4A. An aerial unit comprises a symmetrical arrangement of two flat conductive surfaces disposed in dihedral formation and having a flattened apex, a radiating slot formed along said apex, and a cylindrical reflector inside said dihedron, its axis being parallel to said apex. In an embodiment, three slotted dihedra 9, 10, 11, Fig. 2, are symmetrically disposed around a cylindrical supporting mast 8, which acts as a reflector. The slots are supplied at their centres with equal co-phasal powers, to provide an omni-directional radiation pattern. The internal angle of the dihedra is from 90 to 100 degrees. The length of the slots is approximately X (X = wavelength at the mean frequency of transmission) and their width is X/10. The diameter of the mast 8 is approximately 2X/3 and the distance between the slots and the mast is X/3. Pairs of conductive supports attach the three dihedra 9, 10, 11 to the mast 8, the upper members 15, 16, 17 of which are seen in Fig. 2. These supports are positioned at voltage nodal points on the dihedral plates, and they provide short-circuits for the ends of the slots, which may therefore be left open. Radome devices 17, 18, 19 protect the slots against frost. Several stages of slotted dihedra may be provided, one above the other, to boost the gain of the aerial. The dihedra around the mast may be supplied with power inputs which differ in amplitude or phase, if a directional radiation pattern is required. The slots in the dihedra may be of non-uniform width over their length, in order to improve impedance matching over a wide frequency band (Fig. 3, not shown). In another embodiment, a part cylindrical reflector is provided behind a slotted dihedron (Fig. 1, not shown).