A novel slot antenna that consists of an H-shaped slot encompassed by a rectangular metallic wall and a pair of C-shaped slots outside the wall is proposed. It features a unidirectional pattern, small electrical dimensions and medium gain. The H-shaped slot radiates as an inductively loaded magnetic dipole while the induced electric currents on the vertical wall radiates as electric dipoles. The Front-to-Back Ratio (FBR) of the antenna can be controlled by proper constructive and destructive interferences of radiating fields of the magnetic and electric dipoles.