Several types of aerial producing fan-beam radiation patterns with horizontal polarization are discussed from the aspect of side-lobe suppression in the horizontal plane—which is the plane of narrow beam-width. The theory of the primary feed requirements of cheese and half-cheese aerials is outlined, and the effect of the secondary radiator on the radiation pattern of the primary feed—and so on the distribution of energy across the aperture—is analysed.The factors contributing to side-lobe amplitude in the radiation pattern of the symmetrical cheese aerial are discussed in detail, and it is shown that this type of aerial has side lobes which are large compared with those of the half-cheese aerial and which cannot be reduced much more than 23 db below the main beam level.The design and performance of a half-cheese aerial having maximum side lobes some 30 db below the main beam level are described. The mechanical design and the matching of both cheese and half-cheese aerials are commented upon, and the factors influencing the choice between these two aerials are summarized.