GB1268121A - Improvements in and relating to directional antennas - Google Patents

Abstract

1,268,121. Aerials. H. W. EHRENSPECK. 14 Oct., 1969, No. 50301/69. Heading H4A. A directional aerial comprises a cavity resonator having two reflectors with an interposed feed element, and one or more wave-guiding structures disposed outside the resonator in the radiation direction. The axis of the resonator coincides with the axis of the guiding structure, or with the axis of symmetry of the structures if there is more than one. As described, a dipole primary element F, Fig. 6, is positioned between a full reflector M 3 and a partial reflector M 4 formed by a combination of three rods R, S, T, and a slow wave endfire structure D, formed by seven directors D 2 to D 8 , is positioned adjacently outside said partial reflector. The space between the two reflectors constitutes a resonant cavity, which may be tuned for optimum performance over a wide band of frequencies by mechanically adjusting the relative positions of said reflectors. The aerial impedance may be matched to that of the feed by varying the spacing of the dipole F from the reflector M 3 . Said reflector is circular, and is provided with a forward-facing rim B. The partial reflector M 4 may also be in the form of a circular plate, but of smaller diameter than the reflector M 3 . The free edge of the rim B may carry a dielectric plate which encloses either the dipole and the partial reflector, or the dipole only (Figs. 3, 4, 5, not shown). In the former case, the partial reflector may be mounted on the dielectric plate, and in the latter case the partial reflector may be carried by rods extending from the rim. A second partial reflector may be provided between the first mentioned partial reflector and the wave guiding structure, in order to increase the bandwidth of the structure (Fig. 2, not shown). In another embodiment, a primary element F, Fig. 7, is a broadband " bow-tie " dipole, a main reflector M 3 is square-shaped with a rim B extending only along the two edges parallel to the dipole F, and a partial reflector M 4 is a small circular disc. Two slow-wave endfire structures D are disposed one above the other, and each comprises a set of directors D 2 ... D 4 , .... Alternatively, the two slowwave endfire structures may be disposed side-by-side (Fig. 9, not shown) or four such structures may be arranged with two side-by-side and the other two one above the other (Fig. 10, not shown). If circularly or elliptically polarized waves are to be received or transmitted a crossed dipole feed means may be provided and four slow wave endfire structures may be symmetrically disposed in relation to the axis of the aerial (Figs. 11, 12, not shown).