A simple method is described for analysis of a slot antenna on dielectric substrate of finite thickness. The method consists in using several transformations for reducing the original structure to approximately complementary/dual structure; i.e. to a cylindrical dipole of circular cross-section with a coaxial magnetic cover. The structure thus obtained is then analysed using well-known methods. A model of the slot on dielectric substrate fed by a coplanar waveguide was realised, and experimental results for slot impedance agreed well with the theory.