GB631662A - Improvements in directive antenna systems for defining a path of electromagnetic wave energy - Google Patents

Abstract

631,662. Aerials. SPERRY GYROSCOPE CO., Inc. April 25, 1946, No. 12526. Convention date, April 28, 1945. [Class 40 (vii)J An aerial system having two partially-overlapping directive patterns comprises two cylindrical concave reflectors juxtaposed end-to-end with a primary aerial element opposite each reflector and flat end walls extending perpendicular to the lengths of and bounding the non-proximate ends of the reflectors which form in conjunction with the edges of the reflectors an aperture, common to the two reflectors. The invention is described as applied to an equisignal glide-path system in which the two overlapping beams are modulated with different frequencies. As shown in Fig. 3, the system comprises two cylindrical concave reflectors 25 and 26 with end walls 23 and 22 and a common partition 24, the two reflectors being energized by wave-guide apertures 33,.34 located at the foci. Reflector 25 is parabolic and produces a symmetrical beam 11, Fig. 1, and reflector 26 has an upper parabolic portion 28 and a lower circular portion, thus producing a cosec<2> beam 10, the two beams overlapping in the vertical plane to define a glide-path, 12, the elevation of which may be adjusted by tilting the two reflectors relatively to each other, Fig. 3A (not shown), or by tilting the combined assembly, Fig. 6 (not shown); in a modification of the latter embodiment the reflectors are so shaped that the aperture is still vertical, Fig. 7 (not shown). Any secondary lobes 13, 13<1> associated with the symmetrical beam 11 are encompassed by the cosec<2> beam 10, thus preventing the formation of false equi-signal lines. The partition 24 does not extend from the concave reflecting surfaces as far forward as the end plates 22, 23 so that the two reflectors have a common aperture, thus ensuring that the horizontal projections of the two beams are substantially coincident, Fig. 2 (not shown). The common aperture may be constricted by the addition to the end-plates 22, 23 of tapered sections 36, 36<1>, Fig. 9 and Fig. 8 (not shown), which serve to match the aperture to the reflectors and to attenuate spurious modes generated at the front edge 43 of the partition 24. The formation of secondary lobes is reduced by adding flared flaps 44, 46. In a modification, Fig. 10 (not shown), the two reflectors are of different height and in Fig. 11 (not shown) half-sections of the reflectors shown in Fig. 3 are employed.