GB1413041A - Dipole aerial - Google Patents

Abstract

1413041 Aerials MEL EQUIPMENT CO Ltd 7 Feb 1973 6040/73 Heading H4A Each arm of a dipole aerial is coplanar with a respective outer conductor of a triplate transmission line, one arm being connected to a centre conductor of the line, and the other arm being connected to an outer conductor of the line. Each outer conductor has one or more edge portions substantially forming a line reflector parallel to the dipole. Corresponding points of the two outer conductors adjacent the said edge portions are electrically interconnected by members which extend therebetween, and which are spaced apart by intervals of less than a quarter-wavelength at the mid-band operating frequency of the dipole. As described two dielectric material sheets 1, 2 which are initially completely clad with copper foil on both sides are processed by standard printed circuit techniques to provide conductive patterns as shown. On the outer face of the sheet 1 the foil is shaped to form one outer conductor 3 of a triplate transmission line, and two corresponding dipole arms 5A, 6A, each connected to the outer conductor. The foil is entirely removed from the inner face of the sheet 1. On the outer face of the sheet 2 the foil is shaped to form the other outer conductor 4 of the triplate transmission line and two other corresponding dipole arms 5B, 6B. These arms are separated from the outer conductor by narrow gaps 5C, 6C. On the inner face of the sheet 2 the foil is shaped to form the inner conductor 7 of the triplate transmission line, leading to a first port of a four-port hybrid ring 8 acting as a power divider. Second and third ports of the hybrid ring are respectively connected to one arm of each dipole, and a fourth port is connected to a central pill-shaped resistive matching load. The connections to the dipoles are made through quarter wavelength matching sections 11, 12 leading to higher impedance sections 13, 14, the ends of which are respectively connected to the arms 5B, 6B by rivets passing through the sheet 2. The two inner faces of the sheets are placed together and they are mechanically connected together by rivets around the edges of the outer conductors, which are thereby electrically connected together. The rivets are spaced at intervals of less than a quarter wavelength, and are arranged to be well clear of any part of the central conductive pattern (Fig. 4 not shown). Edge portions 15 of the outer conductors 3, 4 serve as reflectors for the dipoles, and directors may also be provided. The aerial may be mounted within a relatively slim radome on the outside of an aircraft. The radome may be filled with foamed dielectric material, and a layer of R.F. absorbing material may be put between the aerial and the skin of the aircraft.