GB739618A - Antenna feed systems - Google Patents

Abstract

739,618. Aerials. RADIO CORPORATION OF AMERICA. Jan. 13, 1954 [Jan. 30, 1953], No. 1036/54. Class 40 (7). The feed point of an antenna array having a plurality of elements occupying an aperture a plurality of wavelengths long is displaced from the centre of the aperture by more than 5 per cent of the total aperture length and equal amounts of energy are fed to the two groups of elements on the two sides of the feed point. The arrangement may be adjusted so that a vertical aperture gives a substantially cosecant distribution pattern over a desired service area. In one embodiment a slotted cylinder 31 is mounted vertically and the slots 33 are arranged 3 in each of a number of layers with adjacent layers staggered by 60 degrees to ensure uniform illumination in a horizontal plane. The feed to the array is by coaxial feeder 35, 37, led centrally up the lower part of the structure to a point # below the half-way position. At this point the outer conductor is left open and the inner conductor 37 connected to a rod or tube element 39 extending centrally up the cylinder 31 to the top of the system. Thus the feeder 35, 37 is coupled to two coaxial transmission lines 31, 39 and 31, 35 feeding the upper and lower groups of slots respectively. The ends of these lines are each shorted at 43, preferably by a spoke arrangement to allow the antenna to be ventilated. Each slot is coupled to its transmission line by a coupling loop 41 have integrally arranged capacitive or inductive reactance which is adjusted to make the slot appear as a load impedance of a desired magnitude. It is arranged that the impedance presented by all the slots above the feed point taken together is the same as that presented by those below. This causes the upper part of the aerial regarded separately to radiate in a narrower vertical pattern than the lower part although the energy radiated is the same. Partial elimination of nulls results from the combination of the two patterns (Fig. 5, not shown). The elements need not be regularly spaced along the length of the tube providing the aperture length is adequately covered.