GB663924A - Directive antenna system - Google Patents

Abstract

663,924. Aerials. RADIO CORPORATION OF AMERICA. Feb. 25, 1949 [Feb. 27, 1948], No. 5201/49. Drawings to Specification. Class 40 (vii). A directive antenna system of the type including a radiator device in such position in front of a reflector that it partially intercepts the energy reflected therefrom, comprises means for radiating auxiliary energy from the radiator device in substantially the same direction as that from the reflector, to compensate for this shadow effect. The embodiment of Fig. 1 (not shown), comprises a " pill-box " reflector having energy fed thereto by a perpendicular wave-guide with a right angle bend near the open end and a narrow horizontal slit in the wall on the side away from the opening. The size of the slit is such that the amplitude of auxiliary radiation is equal to that of the masked radiation, and the phase is corrected by providing a dielectric body to cover the slit. Fig. 4 (not shown), illustrates the invention applied to a coaxial feeder where the central conductor projects into the reflector at its focus and is backed by a small semi-cylindrical reflector. In this case a slit is made in the small reflector and is again covered by a dielectric body to introduce the required phase delay. The invention is also applicable to the so-called " rear-feed " where a wave-guide extends through a reflector along the directive axis and has a cap at its open end to reflect energy back to the main reflector. In this case a small opening is made in the cap to radiate the same power as is intercepted by the device, Fig. 5 (not shown), and phasing is carried out either by a covering of dielectric as before or by designing the opening to act as a wave-guide near its cut-off frequency, thereby introducing a phase advance. A procedure for determination of optimum slit size and dielectric thickness is described in which the aerial system is used for reception on a secondary lobe and adjustments are made to give minimum response.