We have investigated a folded inverted-L antenna (FILA) and introduced equations with respect to the limitation of the theoretical bandwidth. The miniaturization of the conventional FILA was not sufficient because the FILA consists of a substrate perpendicular to the ground plane. In this paper, we study two different types of FILAs in order to miniaturize the antenna. The miniaturization ratios of the FILAs with the efficiency bandwidth product (B eta product) are estimated. As a result, a 15.3% improvement in the B eta product was obtained over the conventional FILA.