Patent GB-1310794-A (GB)
Title: Rectilinear polarization antennas
IPC: H01Q21/26
Filed: 1971-06-17
Abstract: 1310794 Aerials. THOMSON CSF 17 June 1971 [17 July 1970] 28573/71 Heading H4A An aerial comprises two like, parallel, side-byside metal tubes 1, 2, Fig. 1, which are closed and connected together at their ends by two metal plates 3, 4, which are perpendicular to their axes. A feed conductor 8, which is the inner conductor of a co-axial cable 5, passes through the tube 1 at an opening 7 and is continued by a connection 10 to a terminating point 9 on the outside of the tube 2. The two tubes are closely spaced, and the aerial functions similarly to a slot in a conductive surface. If the tubes are vertically disposed, the radiated field is substantially horizontally polarized. The distance "k" from the plate 4 to the connection 10 is selected to obtain impedance matching between the cable and the aerial, and typical dimensions for the aerial in terms of the operating wavelength # are: diameter of tubes = 0À06 #, length of tubes = 0À5 #, distance between tubes = 0À03 #. The aerial is particularly applicable to radio beacons of the kind in which an amplitude modulated signal is radiated in a rotating cardioid pattern and a phase reference signal is radiated in an omnidirectional pattern. In one such arrangement four tubes 1, 2, 15, 14 are symmetrically disposed with their axes in square formation and are provided with two common end plates. A co-axial cable in each tube has its outer conductor connected to that tube at an aperture therealong, and its inner conductor extended and connected to the outside of the next tube, going clockwise (Fig. 2, not shown). The pairs of inner conductors 8, 16 and 19, 20 running respectively inside the pairs of diagonally opposite tubes 1, 15 and 2, 14 are connected to corresponding opposite terminals of two hybrid bridge circuits (21), (22), Fig. 3 (not shown). In each hybrid bridge circuit the said opposite terminals are connected by quarter-wavelength arms to a third terminal, from which they are fed in phase with reference signal power. They are connected by respective quarter-and three-quarter-wavelength arms to the other (fourth) bridge terminal, from which they are fed in anti-phase with modulated power for the rotating pattern signal. More than one set of four tubes may be used, with vertical stacking to obtain increased gain. By introducing a phaseshift between each of the stacked aerials the axis of the radiated lobe may be tilted above the horizon. As shown in Fig. 6, two sets of four-tube aerials are stacked in vertical formation above a circular counterpoise 50. In this arrangement, the omnidirectional field is radiated by three frames of four quadrants, each arranged to form two curved dipoles. For example, at the top the two quadrants 43, 44 form one centre-fed dipole, and the two quadrants 45, 46 form another centre-fed dipole. The ends of the one dipole form two capacitors 52, 53 with the ends of the other dipole. The use of hybrid bridge circuits in the feeding arrangements may be avoided when such separate radiators for the omni-directional field are provided, the coaxial cables being re-arranged so that two pass through one tube, and none through the diagonally opposite tube (Fig. 5, not shown).