GB813613A - Improvements relating to aerials - Google Patents

Abstract

813,613. Aerials. ANTIFERENCE Ltd., and BEST, N. M. July 27, 1956 [July 29, 1955], No. 21958/55. Class 40 (7). An aerial for use with two radial signals of different frequencies, both polarized in the same direction, comprises a first half-wave dipole for the lower frequency which is centre fed and a second shorter half-wave dipole for the higher frequency formed as a continuous conductive element parallel and adjacent to the first and having the same plane of symmetry. The ratio of the two frequencies is limited to the range 1.2: 1 to 4.8: 1 and the length of the second dipole may require modification from the normal resonant length to compensate for the proximity of the other dipole and to take into account the actual frequencies to be used. In a simple embodiment (Fig. 2) elements 21 and 22 form the first dipole and are supported by junction box 24 in which they are connected to a feeder. The junction box is supported by an arm 25 which also carries the single conductive rod 23 forming the second dipole. The rod 23 may be electrically connected to the arm 25. In a modification of this embodiment (Fig. 3, not shown) the second dipole is supported from the first by insulating struts and is not in contact with the support arm. Reflector elements for both frequencies may be added and if the direction of propagation is the same for both frequencies these may be mounted on a common cross-arm. Director elements may also be provided. One way of incorporating director elements into the array is that described in Specification 813,614. To increase the bandwidth at the higher frequency two similar second dipoles may be used mounted close to each other and equi-distant from the first dipole. Reference has been directed by the Comptroller to Specification 759,968.