We show in this letter that, by using an inhomogeneous metamaterial shell, it is possible to achieve highly directive emission with a small antenna aperture. The material parameters of the metamaterial substrate are obtained by a nonmonotonic optical transformation. Therefore, a large antenna can be effectively transformed to an equivalent one with much smaller aperture. Full-wave finite-element modeling has been performed to confirm this point. The concept proposed here provides a possible solution to reduce the size of antenna without disturbing the radiation characteristics.